







Class TK s.SlI 

Book._ -his 

Copyright N°._ 


COPYRIGHT DEPOSIT. 













DYNAMO TENDING 
for ENGINEERS 

Or, Electricity for Engineers 


CONTAINING A CLEAR AND COMPREHENSIVE TREATISE ON THE 
PRINCIPLES, CONSTRUCTION AND OPERATION OF DYNAMOS, 
MOTORS, LAMPS, STORAGE BATTERIES, INDICATORS AND 
MEASURING INSTRUMENTS AS WELL AS FULL EXPLANATION 
OF THE PRINCIPLES GOVERNING THE GENERATION OF ALTER¬ 
NATING CURRENTS, AND A DESCRIPTION OF ALTERNATING CUR¬ 
RENT INSTRUMENTS AND MACHINERY. 


BY 

HENRY C. HORSTMANN 

and VICTOR H. TOUSLEY 

« 

AUTHORS OF “MODERN WIRING DIAGRAMS AND DESCRIPTIONS 
FOR ELECTRICAL WORKERS” 


ILL UST R A TED 



CHICAGO 

FREDERICK J. DRAKE & COMPANY 

PUBLISHERS 

1904 


















i I 



LIBRARY of CONGRESS 
Two Copies Received 

APR 11 1904 

Copyright Entry 

/ vi"- / ^ 0 4" 

CLASSy ^ XXc. No. 

S L l S' Ur 

COPY B 


COPYRIGHT, 1904 
BY 

FREDERICK J. DRAKE & COMPANY 
CHICAGO, U. S. A. 




• 4 4 • * • 

* • • * 

























INTRODUCTORY 


There are, perhaps, but few engineers who have not 
in the course of their labors come in contact with elec¬ 
trical apparatus such as pertains to lighting and power 
distribution and generation. 

At the present rate of increase in the use of electri¬ 
city it is but a question of time when every steam 
installation will have in connection with it an electrical 
generator. Even in such buildings where light and 
power are supplied by some central station, it is essen¬ 
tial that the man in charge of boilers, elevators, etc., 
be familiar with electrical matters, and it cannot well 
be other than an advantage to him and his employers. 

It is with a view of assisting engineers and others to 
obtain such knowledge as will enable them to intelli¬ 
gently manage such electrical apparatus, as will ordi¬ 
narily come under their control, that these pages have 
been written. 

Within the limited space to which a work of this 
kind is necessarily confined, it has not been possible to 
treat all subjects as extensively as might be desired. 
For rules governing the installation of wires in regard 
to fire hazard the reader is referred to the “Rules and 
Requirements of the National Board of Fire Under¬ 
writers,” and for more extended information in special 
lines, to the various works quoted in the text of this 
book. 

It is hoped that this book will not be considered as 
containing all information needed, but rather that it 
may serve as a stimulus for further study and research. 

3 


4 


INTRODUCTORY 


In this age of progress the man who does not know 
more to-day than he did yesterday and does not con¬ 
tinue to learn every day is soon a back number. The 
world will have but little use for him and treat him 
accordingly. 

That this work may assist many to keep in the van 
is*the earnest wish of 


THE AUTHOR. 


INDEX 


ELECTRICITY FOR ENGINEERS 


Ammeters, 137. 

alternating current, 143. 
shunt, 138. 

Ampere, definition of, 7. 
hour, definition of, 9. 
milli, definition of, 10. 
turns, definition of, 42. 

Arc Lamp, alternating current, 
168. 

brush, 155. 
constant current, 154. 
constant potential, 165. 
enclosed, 167. 
principle of, 153. 
Thomson-Houston, 160. 
Western Electric, 169. 
Armature, location of faults, 61. 

Balanced three-wire system, 
23. 

Booster, 198. 

Brush system, 77. 

controller, 84. 

Brushes, care of, 53. 
construction of, 53. 
shifting of, 62. 
setting of, 59. 
staggered, 55. 

Calculation of wires, 25. 

Center of Distribution, 25. 
Circuit breakers, 117. 

Circular mil, definition of, 26. 
Collector rings, 125. 

Coulomb, definition of, 10. 
Commutator, area allowed for 
current, 51. 
care of, 53. 
construction of, 49. 
Conductivity, definition of, 16. 
Conductors, 7. 

Constant current system, 20. 


Constant potential system, 20. 
Current, 5. 

generation of, 40. 
single phase, 129. 
two and three phase, 130. 
Cut-out box, 25. 

Distributing center, 24. 

Divided circuits, 16. 

Dvnamos, alternating current, 

122 . 

brush, 77. 
care of, 64. 
compound wound, 47. 
failure to generate, 67. 
operation of constant cur¬ 
rent, 75. 

operation of constant poten 
tial, 65. 

operation in parallel, 69. 
reversal of current, 44. 
separate exciting, 123. 
series, connections of, 45 ^ 
shunt, connections of, 46. 
test for polarity, 70. 
Thomson-Houston, 89. 

Electromagnet, 41. 
Electromotive force, definition 
of counter, 108. 
Electroplating, 199. 
Electrolysis, 199. 

Electrolytic action, 9. 
Equalizer bar, 72. 

Feeders, 24. 

Fuses, 117. 

Gramme Ring, 44. 

Ground detectors, 185. 

Heating by electricity, 201. 
Horse power, 15. 


i 


INDEX 


II 

Incandescent lamps, 172. 
current required, 175. 
efficiency tables, 173. 

Insulators, 7. 

Joints in wires, 31. 

Joule, 15. 

Kilowatt hour, 15. 

Laminated armature, 53. 

Light, absorbtion of, 176. 

Lightning arresters, 204. 
Thomson, 206. 

Lines of force, definition of, 41. 
direction of, 42. 

Loss in wires, 27. 

Magnet, soft iron, 5. 
steel, 5. 

Meters, reading of, 147. 

Mil, circular, 26. 
square, 26. 

Motors, 107. 

alternating current, 116. 
compound, 112. 
series, 111. 
shunt, 110. 

Multiple arc system, 20. 

Multiple series system, 21. 

Negative wire, 23. 

Nernst lamp, 177. 

Neutral point of dynamo, 49. 

Neutral wire, 22. 

Ohm, 13. 

Ohm’s law, 14. 

Parallel system, 19. 

Photometer, Bunsen, 190. 
Rumford’s, 191. 

Polarity indicator, 142. 

Positive wire, 23. 

Potential, difference of, 10. 

Prony brake, 187. 

Regulator, Brush, 85. 
series dynamo, 45. 


Resistance box, 46. 
definition of, 13. 
effect of heat on, 13. 

Rheostat for shunt dynamo, 66. 

Series arc system, 20. 
circuit, 6. 

multiple system, 20. 

Service wires, 25. 

Short circuit, 11. 

Speed controller, 114. 

Square mil, 26. 

Static electricity, 12. 

Storage batteries, 193. 

connections for, 197. 
Switchboard, arc, 101. 
arc, 104. 

constant potential, 73. 

Testing lines, 181. 

dynamo efficiency, 187. 
grounds, 184. 
open circuits, 181. 
short circuits, 183. 
Thomson-Houston system, 89. 

controller, 97. 

Three-wire system, 22. 
Transformer, principle of, 130. 
rotary, 128. 

Volt, definition of, 10. 
Voltameter, 9. 

Voltmeter, 10. 

alternating current, 143. 
magnetic vane, 137. 

Weston, 133. 

Watt, definition of, 14. 

hour, definition of, 15. 
Wattmeters, 144. 

Thomson, 145. 

Wires, carrying capacity of, 38. 
properties of, 39. 
weights of copper, 37. 

Wiring tables, 32. 

Wiring systems, 19. 


Electricity for Engineers 

CHAPTER I 

The Electric Current—The Ampere—The Volt—The Ohm—The 

, Watt—Divided Circuits. 

The Electric Current. All electrical phenomena with 
which we have to deal are produced through the 
medium of the electric current. This current flows 
only in a conductor of electricity. Among the most 
noteworthy of the conductors are the various metals; 
the most useful, and in fact the only one in general 
use for light and power purposes, being copper. 

Every conductor offers some resistance to the flow 
of current, just as every pipe offers resistance to the 
flow of steam or water. Just how this resistance varies 
we shall see later on. In order to familiarize ourselves 
with the most important electrical phenomena let us 
consider Fig. I. The current is assumed to leave the 
battery at the +, or positive, pole and flow along the 
wires, etc., to the negative, or — pole, and as it passes 
through the coils of wire wound about the iron bar it 
produces magnetism in the bar. If the bar is of soft 
iron the magnetism lasts only while the current is 
flowing, but a bar of hardened steel will permanently 
retain its magnetism. The current will also heat the 
incandescent lamp until it emits light, and the fine 
wire, R, to the melting point, if desired. In passing 
through the water in the jar, it will decompose it, 
forming oxygen and hydrogen gas. If, instead of 

5 


6 


ELECTRICITY FOR ENGINEERS 


water, the jar is filled with a proper solution, one of 
the copper plates in the solution will be gradually 
eaten away and the other added to. If we now discon¬ 
nect our wires from the battery and connect i at 2, and 
2 at 1, the chemical action in the jar will be reversed, 
the lamp and fine wire, R, will heat as before, no differ¬ 
ence being noticeable. * The iron bar will also be a 
magnet as before, but the end that before attracted 
the north seeking end of a compass needle will now 
reoel it and attract the south seeking end of the same 



needle. The wire which connects the various devices, 
and the devices themselves, constitutes an electric cir¬ 
cuit, and the current is said to flow in such a circuit 
along the wire, just as water flows in a pipe. The 
solid lines form what is known as a series circuit, 
while the dotted lines form a multiple circuit. In the 
latter case, each piece of apparatus receives current 
independent of the others. In the series circuit the 
same current passes through all. If the small wire a 
is connected to b , no current will flow through R; it 





































ELECTRICITY FOR ENGINEERS 


7 


will all flow through a and b. If the wire X be con¬ 
nected to V, all current will flow through it and none 
through any other part of the circuit. The current 
obeys the same law as does water; it takes the path 
which offers the least resistance to its flow. 

Such substances as effectually prevent current from 
flowing through them are known as insulators. Some 
of them are 


Dry Air, . 
Glass, 

Silk, 

Asbestos, 

Porcelain, 

Cotton, 

Rubber, 


Mica, 

Shellac, 

Oil, 

Paraffine, 

Wool, 

Paper, 

Gutta Percha, 


and because the following substances have a low resist¬ 
ance they are known as conductors of electricity. 
Their relative conductivity is in the following order, 
silver being the best: 


Silver, 

Copper, 

Gold, 

Platinum 

Iron, 

Tin, 

Lead, etc. 


The Ampere. The ampere is the unit of volume or rate 
of flow, and in speaking of a flow of so many amperes, 
we mean substantially the same thing, electrically 
speaking, as though we referred to so many gallons of 
water, mechanically speaking. The number of amperes 
flowing over a wire deliver power, much or little, pro- 


8 


ELECTRICITY FOR ENGINEERS 


portional to the electromotive force or pressure under 
which they flow; just as the number of gallons of water 
flowing through a pipe toward a water wheel deliver a 
large or small quantity of power to the wheel, propor¬ 
tional to the pressure under which the water flows. If 
ioo amperes were flowing at a pressure of 10 volts they 
would produce the same power as though there were 
io amperes flowing at ioo volts, exactly as ioo gals, of 
water flowing at a pressure of io lbs. to the square inch 
would produce the same power as io gals, flowing at a 
pressure of ioo lbs. to the square inch. In both cases, 
however, for convenience, we have not considered the 
size of either wire or pipe, but with the wire, as with 
the pipe, as we increase the diameter we decrease the 
friction or resistance. In speaking of the gallon we, 
of course, have something material on which we can 
base the unit gallon. We may take a vessel i ft. wide, 
i ft. long and I ft. high, and this vessel will hold I ,cu. 
ft. of water. This cubic foot would contain 7^4 gals.; 
but in the case of the ampere we must adopt another 
method. We shall take an earthenware tank in which 
is contained a solution of copper sulphate and add one- 
tenth of one per cent, sulphuric acid. We shall next 
take two copper plates and hang them into this solu¬ 
tion, keeping them spaced one inch apart, vertically. 
Having washed these plates in clear water, rounded off 
the corners and dried them thoroughly, we must next 
weigh them very carefully before submerging them in 
the liquid. We may now connect both plates to a 
source from which we can obtain a current of electri¬ 
city and allow the current to flow from one plate to 
another, through the liquid, for a period of time which 
we must measure by a watch or clock. After current 
has flowed for several hours we will remove the plates, 


ELECTRICITY FOR ENGINEERS 


9 


wash them in clean water, and then dip in a bath of 
water containing a very small amount of sulphuric acid 
to prevent oxidization, dry them and carefully weigh 
them again. It will be found that the negative plate 
has increased in weight by what is called electrolytic 
action. Now weigh the negative plate and ascertain 
the exact number of grammes of copper deposited on 
its surface, or, in other words, find how many grammes 
heavier the plate is now than it was before it went into 
the bath. With these data in our possession we will 
multiply the time in seconds that current was passing 
through the plates by .000329 and divide the number 
of grammes deposited on the plate by the result. The 
quotient will be the number of amperes that passed 
from plate to plate. This I give simply to show you 
the manner in which the ampere can be ascertained. 
It is that current which will deposit .000329 gramme 
per second on one of the plates of a voltameter, as 
above described. It is also the current produced by 
one volt acting through a resistance of one ohm. 

In other words, the ampere is that current which 
would be forced over a wire having a resistance of one 
ohm by a pressure of one volt. 

The ampere-hour is the unit of electrical quantity in 
general use. It is the quantity of electricity conveyed 
by one ampere flowing for one hour, or one-half 
ampere flowing for two hours; or again, one-fourth 
ampere flowing for four hours. In each case the sum 
total would be one ampere-hour. It must, however, 
be noted that an ampere-hour with the pressure at no 
volts would deliver just one-half as much power as an 
ampere-hour at 220 volts. 

An ordinary 16 candle-power no volt incandescent 
lamp requires a current of about one-half an ampere, 


10 


ELECTRICITY FOR ENGINEERS 


while a lamp of the same candle-power at 220 volts 
requires but one-fourth of an ampere, and a 52 volt 
lamp about one ampere. 

A milli-ampere is the one-thousandth P art 

an ampere. 

The Coulomb. The Coulomb is the unit of quantity. 
It is the quantity of current delivered by one ampere 
flowing for one second. 

The Volt. By electromotive force, volts, or.potential, 
we mean electrically about the same as we do when 
speaking of pounds pressure as indicated on a steam 
gauge. If we connect a volt-meter between a positive 
and a negative wire we find that it indicates a certain 
number of volts; the volt-meter then indicates electrical 
pressure just as a steam gauge indicates steam pressure. 
The difference in potential or pressure between two 
wires vve will assume to be 100 volts, and the difference 
of potential between the inside of a pipe and the atmos¬ 
phere also at 100 lbs. to the square inch. The steam 
gauge is closed at one end of the tube which operates it, 
and hence, the pressure from the interior of the pipe 
does not flow into the atmosphere; in other words, the 
resistance offered to the pressure prevents the water 
from escapin-g into the atmosphere. In the case of 
the volt-meter the resistance of the wires used in its 
construction prevents any great quantity of electricity 
from flowing out of the positive wire and into the 
negative through the volt-meter coil. If the gauge 
were accidentally broken off the pipe, the resistance to 
the pressure on the inside of the pipe would be greatly 
lowered and allow the water to flow into the atmos¬ 
phere. If a piece of ordinary wire were connected to 
the positive and negative wires, where we have just 
connected our volt-meter, it would form a path of such 


ELECTRICITY FOR ENGINEERS 


11 


low resistance and allow all the current to flow through 
it, so there would be no pressure indicated in the volt¬ 
meter. This would be called a “short circuit.’ ’ With 
a volt-meter there is always a small amount of current 
flowing from a positive to a negative wire through the 
coil in the meter. This current is neccesary to produce 
the reading on the meter, but we need not consider 
this current at present, the quantity being very small. 

One volt (unit of pressure) will force one ampere 
(unit of current) over one ohm (unit of resistance). 

Potential is a term quite frequently used to express 
the same idea as voltage or electromotive force, but its 
meaning is somewhat different. Suppose that a steam 
engine is working with ioo dbs. of pressure at the 
throttle valve, and exhausting into a heating system or 
system of piping that offers a back pressure of 5 lbs. to 
the square inch; in other words, the resistance to the 
flow of steam out of the exhaust pipes of this engine is 
such that the remaining pressure, when the engine has 
exhausted, is 5 lbs. Now it will readily be seen that 
the total pressure utilized to do the work would be 100 
lbs. less 5 lbs., or 95 lbs., and therefore the potential 
would be 95 lbs. Now, if we are using electricity at 
100 volts pressure, and lose 5 volts in overcoming 
resistance, we have a potential of 95 volts left. When¬ 
ever work is done by a steam engine a certain amount 
of pressure is lost by condensation, doing work and by 
overcoming friction. This loss may be considered the 
same as a loss of potential, for in the use of electricity 
any loss in pressure of volts that may occur from 
doing work or overcoming resistance is called a loss of 
potential. 

In open arc lamps the loss of potential across the 
terminals or binding posts is about 50 volts; that is, 50 


/ 


12 


ELECTRICITY FOR ENGINEERS 


volts have been absorbed or used in producing light. 
You can now readily understand that electromotive 
force means force, pressure, energy, and that by 
potential we mean the capacity to do work or the 
effective pressure to do work. While we are speaking 
of electromotive force we may consider some of the 
advantages of high and low electromotive forces. 
High electromotive force, like steam at high pressure, 
is far more economical in transmission or utilization 
because the quantity may be that much smaller. 

When transmitted to great distances, high electro¬ 
motive forces, like high water or steam pressures, are 
far more desirable on account of the reduction in fric¬ 
tion losses; but this is partially offset by the necessity 
of using, in water transmission, a much stronger pipe 
for the high pressure than would be necessary for the 
low pressure, and in the transmission of current at a 
high electromotive force or pressure it becomes neces¬ 
sary to use wires with far better insulating material 
than would be required for the transmission of elec¬ 
tricity at low pressure. Increasing the pressure or 
electromotive force always means more danger, even if 
you know the pipes are extra strong or the insulation 
of the wire is of unusually high resistance; for if any¬ 
thing should happen the consequences would be far 
more serious with high than with low pressures. But 
notwithstanding all this, engineers are continually 
increasing the pressures of electrical machinery. 

Static electricity is a term applied to electricity pro¬ 
duced by friction, and a static discharge of electricity 
usually consists of an infinitely small quantity but a 
very high electromotive force or pressure. Discharges 
of lightning are extremely high in voltage, but the 
quantity of current that flows is very small. 


ELECTRICITY FOR ENGINEERS 


13 


The Ohm. The ohm is the unit of resistance. Resist¬ 
ance, electrically speaking, is much the same thing as 
friction in mechanics. If a wire or pipe of a certain 
length is delivering io gals, or io amperes at a pressure 
of ioo lbs. or ioo volts, and we propose to double the 
flow without increasing the pressure, it will be necessary 
for us to increase the diameter of the pipe and wire in 
order to lower the resistance of the wire and the friction 
of the pipe to one-half of what it was before. If we 
desire the best results from the pipe, we lower its fric¬ 
tion by reaming out all burrs and avoiding all unneces¬ 
sary bends and turns; likewise if we desire the best 
results from the wire we will have the copper of which 
it is constructed as nearly pure as possible, and we 
will install the wire where its temperature will not be 
unnecessarily high, avoiding boiler rooms and other 
hot places. Resistance of the wire increases slightly 
with an increase in temperature. 

For every additional degree centigrade the resistance 
of copper wire increases about 0.4 per cent., or for 
every additional degree Fahrenheit about 0.222 per 
cent. Thus a piece of copper wire having a resistance 
of 10 ohms at 3 2° F. would have a resistance of 11.IG 
ohms at 82° F. An annealed wire is also of lower 
resistance than a hard drawn wire of the same size. 
A good idea of the value of an ohm may be had from 
the following table, which gives the length of differ¬ 
ent wires required to make one ohm resistance. 

FEET PER OHM OF WIRE (B. & S.). 


04 feet of No. 

20 

605 feet of No. 

12 

150 

18 

961 “ 

10 

239 

16 

1529 

8 

380 

14 

2432 

6 


3867 feet of No. 4 


14 


ELECTRICITY FOR ENGINEERS 


We have not as yet established a unit of mechanical 
friction, therefore when we speak of mechanical fric¬ 
tion we refer to it as requiring a certain quantity of 
power to overcome it. When, however, resistance to 
the flow of electricity is spoken of it is referred to as 
so many ohms. It can be measured in several ways, 
the most reliable and convenient being by an instru¬ 
ment called the Wheatstone Bridge. It can also be 
calculated if the length and diameter of the wire or 
conductor is known, as will be shown later on. 

The basis of all electrical calculation is Ohm’s law. 
This law reads: 

“The strength of a continuous current in a circuit is 
directly proportional to the electromotive force acting 
on that circuit, and inversely proportional to the resist¬ 
ance of the circuit.’’ In other words, the current is 
equal to the volts divided by the ohms. Expressed in 
symbols, C = E/R; C being current, E voltage, and R 
resistance. If an incandescent lamp having a resist¬ 
ance of 200 ohms be placed in a socket where the 
pressure is 115 volts, the resulting current through 
such a lamp would be 115 divided by 200, or .575 of an 
ampere. 

From the formula C = E/R, two others are deduced. 
The volts divided by the amperes equal the ohms, 
E/C = R. 

The amperes multiplied by the ohms equal the volts, 
CxR=E. 

The Watt. The watt is the unit of power. It is an 
ampere multiplied by a volt; just as the unit of mechan¬ 
ical power, called the foot pound, is the result of the 
pound multiplied by the space in feet through which it 
moves. If a current of say 100 amperes, flows over a wire 
at a pressure of 10 volts, the power delivered will equal 


ELECTRICITY FOR ENGINEERS 


15 


ioo amperes x io volts = 1,000 watts. If a current of 
io amperes flows over a wire at a pressure of ioo volts, 
the power would be exactly the same, io amperes x ioo 
volts, or i,ooo watts. But, of course, in the first case it 
would require a wire ten times as large to deliver the 
1,000 watts as would be necessary in the latter case. 
If a weight of io pounds were being elevated through 
space at the rate of ioo ft. per minute the power 
equivalent would be io lbs. x ioo ft., or i,ooo ft. lbs. 
If an arc lamp consumes io amperes at a pressure of 
70 volts, its power consumption is 10 x 70, or 700 watts. 
One watt is the power developed when 44.25 ft. lbs. 
of work are done per minute. Seven hundred forty- 
six watts equal one horse power. The watt-hour 
is the unit of electric work, and is a term employed to 
indicate the expenditure of one watt for one hour. 
The kilo watt-hour is the term employed to indicate 
the expenditure of an electric power of 1,000 watts for 
one hour. 

The work done per second when a power of one watt 
is being developed is called the joule, and a joule is 
equal to .7375 ft. lbs. 

Electromotive force times current equals watts. 
The square of the current multiplied by the resistance 
equals watts; and the voltage multiplied by itself and 
divided by the resistance equals watts. Expressed in 
symbols, these explanations would look like this: 

W = E x C. W = C 2 x R. W = E 2 - R. 

First. If we have an electromotive force or voltage of 
10 volts and a current of 20 amperes, we have 10 x 20 = 
200 watts. 

Second. If we have a current of 10 amperes and a 
resistance of 30 ohms, we would have 10 x 10 x 30 = 3,000 
watts. 


16 


ELECTRICITY FOR ENGINEERS 


Third. If we have an electromotive force or voltage 
of 10 volts and a resistance of 20 ohms, we would have 
10 x 10, or 100 -4- 20, or 5 watts. 

In the above formulas E stands for voltage, C for 
current, R for resistance and W for watts. 

Divided Circuits. Currents of electricity, although 
they have no such material existence as water or 
steam, still obey the same general law; that is, they 
flow and act along the lines of least resistance. If a 
pipe extending to the top of a ten story building had 
a very large opening at the first floor, it would be im¬ 
possible to force water to the top floor. All the water 
would run out at the first floor. If the opening at the 
first floor were small only a part of the water would 
escape through it, some would reach the top of the 
building. The flow of water in each case is inversely 
proportional to the resistance offered to it by the dif- 
erent openings. 

The same thing is true of currents of electricity. 
Where several paths are open to a current of electri¬ 
city the flow through them will be in proportion to 
their conductivities, which is the inverse ratio of their 
resistances. As an illustration, the current flow 
through all of the lamps, Fig. 2, is the same, because 



FIGURE 2. 


each lamp offers the same resistance. But if we 
arrange a number of lamps as in Fig. 3, the lamps in 
series will offer twice as much resistance as the single 






ELECTRICITY FOR ENGINEERS 


17 



FIGURE 3. 


lamps, and will receive but half the current of the 
single lamp. In Fig. 4 we have still another arrange¬ 
ment. The lamp A limits the current which can flow 
through B and C, and that current which does flow 



divides between B and C in proportion to their con¬ 
ductivities. If B has a resistance of no ohms and C 
220 ohms, then B will carry two parts of the current 
and C only one. The combined resistance of all 
lamps, Fig. 2, equals the resistance of one lamp 
divided by the number of lamps. The combined resist¬ 
ance, Fig. 3, equals the sum of the resistances of the 
two lamps at A multiplied by the resistance of B and 
divided by the sum of all the resistances. If the resist¬ 
ance of each of the lamps were no ohms, the problem 

would work out thus: n7^ fiQ ~ + ~ if5 = 73^- 

In Fig. 4 the total resistance is nT+T§5 + no = 183^. 

One practical illustration of the above law may be 
found in the method of switching series arc lamps, 















18 


ELECTRICITY FOR ENGINEERS 


Fig. 5. As long as the switch S is open the arc lamp 
burns, but as soon as the switch is closed the lamp is 



extinguished because the resistance of the short wire 
and the switch S is so much less than that of the arc 
lamp that practically all the current flows through S. 






CHAPTER II 


WIRJNG SYSTEMS — CALCULATION OF WIRES — WIRING 

TABLES. 

Wiring Systems. The system of wiring which is most 
generally used for incandescent lighting and ordinary 
power purposes is called the two wire parallel system. 
In this system of wiring the two wires run side by side, 
one of them being the positive and one the negative. 
The lamps, motors and other devices are then con¬ 
nected from one wire to the other. A constant pressure 
of electricity is maintained between the two wires, and 
the number and size of lamps, or other apparatus, 
connected to these two wires, determine how many 
amperes are required. Each lamp or motor is inde¬ 
pendent of the others and may be turned on or off 
without disturbing the others. 

A diagram of such a system is shown in Fig. 6. 



0 0 0 0 






FIGURE 6. 


In this system the quantity of current varies in pro¬ 
portion to the number of devices connected to it. 
Suppose that we are maintaining a pressure or poten¬ 
tial or electromotive force of no volts on such a sys¬ 
tem, and that we have connected to the system ten 16 
candle power incandescent lamps, consuming one-half 

19 























20 


ELECTRICITY FOR ENGINEERS 


ampere each. The total quantity of current to supply 
these lamps would be 5 amperes. If we should now 
switch on ten more lamps the quantity of current 
would be 10 amperes, and the pressure would remain 
no volts. This system is also known as the “constant 
potential system,” or multiple arc system, and among 
the numerous devices used in connection with it are 
the constant potential arc lamp, the shunt motor, the 
compound wound motor, the series motor, incandes¬ 
cent lamps, etc. Electric street railways are also 
operated on this system. The electricity supplied 
through this system of wiring may be either direct or 
alternating current. 

The series arc system, Fig. 7, is a loop; the greatest 
electrical pressure being at the terminal or terminal ends 



of the loop. The current in such a system of wiring is 
constant, and the pressure varies as the lamps or other 
apparatus are inserted in or cut out of the circuit. 
This system is also called the constant current system. 
The same current passes through all of the lamps, and 
the different lamps are also independent of each other. 

At the present time the series system is used mostly 
for operating high tension series arc lamps. The use 
of motors with it has been almost entirely abandoned. 

The series multiple system, Fig. 8, is simply a num¬ 
ber of multiple systems placed in series. This method 
of wiring was at one time employed to run incandes- 








ELECTRICITY FOR ENGINEERS 


21 


cent lights from a high tension series arc light circuit, 
but on account of the danger connected with the use 



figure 8. 


of incandescent lamps, operated from a high tension arc 
lamp circuit, the system has been abandoned. It is 
not approved by insurance companies, and conse¬ 
quently is not often used. 

The multiple series system consists of a number of 
small series circuits, connected in multiple, as shown 
in Fig, 9. This system of wiring is used on constant 



potential systems, where the voltage is much greater 
than is required by the apparatus to be used, as, for 
instance, connecting eleven miniature lamps, whose 
individual pressure required is 10 volts, into a series, 
and then connecting the extreme ends of such a series 
to a multiple circuit whose pressure is no volts. In 
electric street cars, where the pressure between the 



















22 


ELECTRICITY FOR ENGINEERS 


trolley wire and the running rail is 500 volts, it will be 
noticed that the lighting circuits in the car consist of 
five 100 volt lamps in series, and one end of this series 
is connected to. the trolley line, the other end being 
grounded on the trucks. 

The three wire system, Fig. 10, is a system of 
multiple series. In this system, as its name implies, 
three wires are used, connected up to the machines in 


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FIGURE 10 . 



the manner shown in the diagram. Both machines are 
in series when all lights are turned on, but should all 
lights on one side of the neutral or center wire be 
turned off the machine on the other side alone would 
run the other lights. 

One of these wires is positive, the other is negative, 
and the remaining one or center wire is neutral. In 
ordinary practice from positive to negative wire, a 
potential of 220 volts is maintained, while from the 
neutral wire to either of the outside wires a potential 
of no volts exists. The advantages of such a system 
are many, principally among them is the use of double 
the voltage of the two wire system; this reduces the 
current one-half and allows the use of smaller wires. 
This system only requires three wires for the same 
amount of current that would require four in the other 
system. Motors are supplied at 220 volts, while 
lights operate at no. Incandescent lighting circuits 




















ELECTRICITY FOR ENGINEERS 


23 


can be maintained from either outside wire to the 
neutral wire. The saving - in copper by dispensing 
with the fourth wire is not the only advantage in the 
saving of conductors. The neutral wire may be much 
smaller than the outside wires because it will seldom 
be called upon to carry much current. 

Inside of buildings, however, where overheating of 
a wire is always dangerous, the neutral wire should be 
of the same size as the others. By tracing out the 
circuits in Fig. io, it will readily be seen that, so long 
as all lamps are burning, the current passes out of 
dynamo i into the positive wire and from there through 
the lamps (always two in series) to the negative 
or — wire, returning over it to the — pole of dynamo 2. 
So long as an equal number of lamps is burning on 
each side of the neutral, no current passes over the 
neutral wire in either direction. But if the positive 
or + wire should be broken, say at a, dynamo i will no 
longer send current and the lamps between the positive 
and neutral wire will be out. 

Dynamo 2 will now supply the lamps between the 
neutral and the negative wire and for the time being 
the neutral wire will become positive. Should the 
negative wire break at b , the lamps connected to it 
would be out and dynamo I would supply the lights on 
its side, the neutral wire becoming negative. When 
motors of one or more H. P. are used on this system, 
it is usual to connect them to the outside wires using 
220 volts. It is important also to arrange the wiring 
so that an equal number of lights are installed on each 
side of the neutral. When the lights and motors are 
so arranged, the system is said to be “balanced.” It 
is also very important to arrange so that the neutral 
wire cannot readily be broken. Should the neutral 


24 


ELECTRICITY FOR ENGINEERS 


wire be opened while, for instance, fifty lamps were 
burning on one side and say ten or twenty on the 
other, the ten or twenty would be broken by the excess 
voltage. Grounded wires ordinarily cause more 
trouble than anything else on electric light or power 
circuits, but with the three wire system, the neutral 
wire is often grounded. Grounds on this wire are less 
objectionable than on other wires, because it carries 
very little current, and that current is constantly vary¬ 
ing in direction, so that no great amount of electrolysis 
can occur at any one place. For full descriptions and 
drawings of methods of wiring, see Wiring Diagrams 
and Descriptions by Horstmann and Tousley, published 
by Frederick J. Drake & Co., Chicago. 

Feeders (see Fig. u), as the name implies, is a term 
used to designate wires which convey the current to 



any number of other wires, and the feeders become a 
part of the multiple series, multiple and three wire 
systems. 

Distributing mains are the wires from which the wires 
entering buildings receive their supply, 
























































ELECTRICITY FOR ENGINEERS 


25 


Service zvires are the wires that enter the buildings. 

The ce?iter of distributio?i is a term used for that part 
of the wiring system from which a number of branch 
circuits are fed by feeder wires. In most buildings 
the tap lines are all brought to one point, and ter¬ 
minate in cut-out boxes. These cut-out boxes are 
supplied by the main. Each floor of the building may 
have a cut-out box, or each floor of the building may 
have several cut-out boxes of the above description. 

Calculation of Wires. If we desire to transmit or 
deliver a certain quantity of liquid through a -pipe, 
we estimate the size of the pipe and 
the comparison of sizes in the pipes 
by squaring the diameter, in inches, 
and multiplying the result by the 
standard fraction .7854. By way 
of explanation we will dwell upon 
the above method for a short time. 

In Fig. 12 we have a surface which 
measures one inch on all four 
sides, and which has an area of one square inch. 

Now in a circle which is contained in this figure, and 
which touches all four sides of the square, we would 
only have .7854 of a square inch. If the diameter of 
this circle is 2 in., instead of 1, you can readily see by 
Fig. 13 that its area is four times as great or 2 x 2 = 4. 
We then multiply by the standard number .7854 in 
order to find the area contained in the two-inch circle; 
and if the diameter were 3 in., then 3x3 = 9, and 
9 x .7854 would be the area in square inches contained 
in the three-inch circle. 

Again, if we had a square one inch in area, like Fig. 
14, and we took one leg of a carpenter’s compass and 
placed it on one corner of this square, striking a 









2G 


ELECTRICITY FOR ENGINEERS 


quarter-circle from one adjacent corner to the other 
adjacent corner, the area inscribed by the compass 
would again be .7854 of a square inch. 

The above will explain to the reader the relation 

1 » 

--- 1 

FIGURE 13 . 

between the circular and square mil. The circular 
mil is a circle one mil an inch) in diameter. 

The square mil is a square one mil long on each side. 
In the calculation of wires for electrical purposes, the 
circular mil is generally used, because we need only 

multiply the diameter of a wire by 
itself to obtain its area in circular 
mils. If we used square mils we 
should have to multiply by .7854. 

The resistance of a conductor ‘ 
(wire) increases directly as its length, 
and decreases directly as its diameter 
figure 14 . is increased. A wire having a diam¬ 
eter of one mil and being one foot 
long has a resistance at ordinary temperature of 10.7 
ohms. If this wire were two feet long, it would have 













ELECTRICITY FOR ENGINEERS 


27 


a resistance of 21.4 ohms, but if it were two mils in 
diameter and one foot long, it would have a resistance 
one-fourth of 10.7, or about 2.67. 

Every transmission of electrical energy is accom¬ 
panied by a certain loss. We can never entirely pre¬ 
vent this loss any more than we can entirely avoid 
friction. But we can reduce our loss to a very small 
quantity simply by selecting a very large wire to carry 
the current. This would be the proper thing to do if 
it were not for the cost of copper, which would make 
such an installation very expensive. As it is, wires 
are usually figured at a loss of from 2 to 5 per cent. 

The greater the loss of energy we allow in the wires 
the smaller will be the cost of wire, since we can use 
smaller wires with the greater loss. 

In long distance transmission and where the quality 
of light is not very important, a loss of 10 or 20 per 
cent, is sometimes allowed, but in stores, residences, 
etc., the loss should not exceed 2 or 3 per cent., other¬ 
wise the candle power of the lamps will vary too much. 

Where the cost of fuel is high the saving in first cost 
of copper is soon offset by the continuous extra cost 
of fuel to make up for the losses in the wires. 

To determine the size of wire necessary to carry a 
certain current at a given number of volts loss, we may 
proceed in the following manner: Multiply the num¬ 
ber of feet of wire in the circuit by the constant 10.7, 
and it will give the circular mils necessary for one ohm 
of resistance. Multiply this by the amperes, and this 
will give the circular mils for a loss of one volt. Divide 
this last result by the volts to be lost, and the answer 
will be the number of circular mils diameter that a 
copper wire must have to carry the current with such a 
loss. After obtaining the number of circular mils 


28 


ELECTRICITY FOR ENGINEERS 


required, refer to the table of circular mils, and select 
the wire having such a number of circular mils. 

The formula is as follows: 


Feet of wire x 10.7 x amperes 
Volts lost 


= circular mils. 


By simply transposing the above terms we obtain 
another formula, which can be used to determine the 
volts lost in a given length of wire of a certain size, 
carrying a certain number of amperes. 

The formula is as follows: 


Feet of wire x 10.7 x amperes 
Circular mils 


= Volts lost. 


And again, by another change in the terms *we 
obtain a formula which shows the numb-er of amperes 
that a wire of given size and length will carry at a 
given number of volts lost: 


Circular mils x volts lost 
Feet of wire x 10.7 


= Amperes. 


In computing the necessary size of a service or main 
wire, to supply current for either lamps or motors, it 
is necessary to know the exact number of feet from the 
source of supply to the center of distribution. When 
the distance of center of distribution is given it is well 
to ascertain whether it is the true center or not. It 
may be only the distance from a cut-out box that has 
been given, when it should have been the distance 
from the point at which the service enters the building 
or, perhaps, from the point at which the service is con¬ 
nected to the street mains. For when the size is deter¬ 
mined it is for a certain loss which is distributed over 
the entire length of the wire to be installed. The trans¬ 
mission of additional current on the mains in the build¬ 
ing increases the drop in volts in the main, and likewise 





ELECTRICITY FOR ENGINEERS 


29 


in the service. Most buildings are wired for a certain 
per cent loss in voltage, estimated from the point 
where the service enters the building. All additions 
should be estimated from that point. 

In using the formula for finding the proper size wire 
to carry current, the first thing to be determined is the 
length of the wire; remember that the two wires are in 
parallel, and therefore the total length of the wire is 
twice the total distance from the commencement to 
the end of the circuit. If the proposed load on this 
circuit is given in lamps, you may reduce it to amperes, 
and if the proposed load is given in horsepower, you 
may reduce it to amperes. The voltage on the circuit 
is known in either case. You take the loss of the 
voltage and divide the product of amperes, multiplied 
by the length, as found, and 10.7 by it; this answer 
will be the size in circular mils of a wire necessary to 
carry the amperes. 

Example: What is the size of wire required for a 50 
volt system, having 100 lamps at a distance of 100 ft., 
with a 4 per cent loss? 

Answer: The load of 100 lamps on a 50 volt system 
is 100 amperes, and a 4 per cent loss of 50 volts is 2 
volts. Multiply the total length of the wire, which is 
twice the distance, or 200 ft., by the 100 amperes of 
current; this gives us 20,000. Then multiply this by 
the constant, which is 10.7; this gives us 214,000. 
Divide this by 2, which is the loss in volts, and you 
have 107,000 circular mils diameter of wire required 

When determining the size of wire to be used it is 
always necessary to consult the table of carrying 
capacities, and this will very often indicate a wire 
much larger than that determined by the wiring for¬ 
mula, especially if a somewhat high loss is figured on. 


30 


ELECTRICITY FOR ENGINEERS 


When estimating the distance it is not always cor¬ 
rect to take the total distance. 

To illustrate: Suppose one lamp is 100 ft. from the 
point at which the distance is determined, and the 
farthest lamp is 400 ft., the remaining lamps being 
distributed evenly between these two points; we would 
average the distances between the first and last lamp, 
which would be 200 ft. It is necessary to use judg¬ 
ment in estimating the mean or average distance, as 
the lamps or motors are bunched differently in each 
case 

In a series system the loss in voltage makes con¬ 
siderable difference to the power, but does not affect 
the quality of the light as much as in a multiple arc or 
parallel system. In a parallel system the lamps 
require a uniform pressure, and this can only be had 
by keeping the loss low. In a series system the lamps 
depend upon the constant current and the voltage 
varies with the resistance, in order to keep the current 
constant. This is accomplished by a regulator on the 
dynamo, which is designed to compensate for the 
changes of resistance in the circuit and to increase or 
decrease the pressure as required. 

In estimating the size of wire for a series system you 
consider the total length of the loop. There is no 
average distance as the total current travels over the 
entire circuit. We will assume that you have an arc 
light circuit of a No. 6 Brown & Sharp gauge wire and 
want to find what loss there is in this circuit. You 
have the area of a No. 6 wire, which is 26,250 circular 
mils, and the length of the circuit, and from this we 
will figure the loss in this manner: Assuming the 
circuit to be 10,000 ft. long, and the current 10 
amperes, we will multiply 10,000 ft. by 10 amperes, 


ELECTRICITY FOR ENGINEERS 


31 


and this by 1.07, which gives us 1,070,000, and divide 
this by 26,250. The answer is 40 volts, lost in the 
circuit. 




Such a circuit would operate at perhaps 2,000 or 
^,000 volts, and a loss of 40 volts would not be exces- 









































32 


ELECTRICITY FOR ENGINEERS 


sive. It would be wasting a little less energy than is 
required to burn one large arc lamp. 

The multiple series system is a number of small wires 
connected in multiple, and is the same as the multiple 
arc or parallel system. The wire is figured in the same 
way as for the multiple arc system. 

The series multiple system is a number of small paral¬ 
lel systems, and these are connected in series by the 
main wire. The wire is figured the same as for the 
series system. 

The Edison three-wire system is a double multiple, and 
the two outside wires are the ones considered when 
carrying capacity is figured. When this system is 
under full load or balanced, the neutral wire does not 
carry any current, but the blowing of a fuse in one of 
the outside wires may force the neutral wire to carry 
as much current as the outside wire and it should, 
therefore, be of the same size. The amount of copper 
needed with this system is only three-eighths of that 
required for a two-wire system. 

Wiring Tables. On the following pages are presented 
wiring tables for 110,220 and 500 volt work. These 
tables are used in the following manner: Suppose we 
wish to transmit 60 amperes a distance of 1,800 ft. at 
no volts and at a loss of 5 per cent. We take the col¬ 
umn headed by 60 in the top row and follow it down¬ 
ward until we come to 1,800, or the number nearest to 
it. From this number we now follow horizontally to 
the left, and under the column headed by 5 we find 
the proper size of wire, which is 500,000 c. m. The 
same current, at a loss of 10, would require only a 0000 
wire, as indicated under the column at the left, headed 
by 10. 

Before making selection of wire, always consult the 


ELECTRICITY FOR ENGINEERS 


33 


table of carrying capacities, page 38. This table is 
taken from the rules of the National Board of Fire 
Underwriters, and is in general use. 

The first three of the following tables are wiring 
tables for the three standard voltages, no, 220, 50c 
From these tables can be found the sizes of wire 
required to carry various amounts of current (in am¬ 
peres) different distances (in feet) at several percent¬ 
ages of loss, or the distance the different sizes of wire 
will carry various amounts of current at several per¬ 
centages of loss can be found. 

These tables are figured on safe carrying capacity for 
the different sizes of wire. The distances in feet are 
to the center of distribution. 


110-VOLT WIRING TABLE. 


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One Horsepower =1.49 amperes. When lights are used the lamps are put in series. 














































































































































c g : : 

mummmmm o O O 

CJ^^WWH-OOCC^CJOl^tOMMOOOO* • • 

Size 

B. & S. 

Gauge 

707 160 

632 455 

547 722 

460 000 

409 640 

364 800 

324 950 

289 300 

257 630 

229 420 

204 310 

181 940 

162 020 

144 280 

128 490 

114 430 

101 890 

90 742 

80 808 

71 961 

64 084 

57 068 

50 820 

Diam. 

Mils 

500000 0 

400000 0 

300000 0 

211600 0 

167805 0 

133079 0 

105592 5 

83694 5 

66373 2 

52633 5 

41742 6 

33102 2 

26250 5 

20816 7 

16509 7 

13094 2 

10381 6 

8231 11 

6529 94 

5178 39 

4106 76 

3256 76 

2582 67 

Circular 

Mils 

Area 

M M M lO CO W 

££ t ^£2 0 JS5°?£ r ' ,:x,0i ‘‘ i — ®ooMMMco(otc®n@o 
00»JO'»103*)Mi(.0'.®^ai4i®OM'1000000 

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Square Mils 

• • • • • |__t »_» 

>-. • to • co- 4-- • os- oMoi®woo-jc>aoo<‘M» 

4- • CO- - • oo- OS • I^COMMMI-‘MOCI105'MO 

Pounds 
per 1000 feet 

Double Braided 

Weather-Proof Wire 

• • • . . i—W M) CO C7* -3 00 

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• • • • • 

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per mile 

OS • 4^- • co to >—* • 

50- 4* • CO- I—- Oi • OQCOSCJ’i^COtOtC — m 

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■ 4^- • ©• !--• o- OMceoowa®-o-jwi4i^® 

Feet per 
Pound 

• • • • • t—i t—» »—L 

* • . * • ^^>--<OtOlOC04s.Oi-'jH-4.~5 

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m- 44.- CO • tO; 4--; tO 4*- to 00 © -J CO © Os tO O’ as. 

Pounds 
per 1000 feet 

Triple Braided 

- • • • • -totococoo'-^e 

_• 4-» • »—• tO- CO- 0>-5CCOCOtnOO)-®a)H>.M 

00- to- -<{• • CO- !D^OnOHti®0®i(--l-0 

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Pounds 
per Mile 

Oi • • CO >— • •— 1 • 

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Feet 

per Pound 

l—l 1—‘ 

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Pounds 
per lOuO feet 

W 

> 

• ►— i >— k M)t'OCOrf^OiQO 

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per Mile 

? 

p 

& 


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Feet 

per Pound 


4. CO tO tO --- f—- 

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-tO)OS®®44'4i4Klt- >H-W®(0®000000-1 
0SO3i*JOM00W®0'000S00t4W(»*JMM4-Cn®® 

R Ohms 
per 1000 feet 

Resistance at 75° F. 

10978! 

13723 
18297 
25891 
32649 
41168 
51885 
65460 
82543 
1 04090 
1 31248 

1 65507 

2 08706 

2 63184 

3 31843 

4 18400 

5 27726 

6 65357 
8 39001 

10 5798 
13 3405 
16 8223 
21 2130 

Ohms 
per Mile 

^►-MMMCOtlsC'ffiODOMOSOCOOOOO 

MMMiMS-lOMO'OS'-OOMOHCCMMOatO 

4-®®M®oa®ot5®to-i®a-iui-}®»M® 
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Feet 
per Ohm 

00001322 

00002063 

( >00036-=>6 

00007653 

00012169 

00019438 

00030734 

00048920 

00077784 

0012370 

0019666 

0031273 

0049723 

0079078 

0125719 

0199853 

0317946 

0505413 

0803641 

127788 

203180 

323079 

513737 

Ohms 
per Pound 


TABLE OF SIZES, MEASUREMENTS, WEIGHTS, ETC., OF COPPER WIRE. 
























































38 


ELECTRICITY FOR ENGINEERS 


& * 'I 

TABLE OF CARRYING CAPACITY OF WIRES. 


ijl 

UNDERWRITERS’ 

RULES. 



Table A. 

Table B. 


if 5 

Rubber 

Other 



Insulation. 

Insulations. 

Circular 

B. & S. G. 

Amperes. 

Amperes. 

Mils. 

;i 18. 

. 3 . 

5 . 

- 1,624 

16. 

. 6. 

8. 

2,583 

14 . 



- 4,107 

12. 

. 17 . 

... 23. 

6,530 

io. 

. 24. 

• •• 32 . 

.... 10,380 

8. 

. 33 . 

... 46 . 


6. 

. 46 . 

... 65. 

. ... 26,250 

5 . 

. 54 . 

... 77 . 

. ... 33 ,ioo 

4 . 

. 65. 


- 4 L 740 

3 .. 

. 76 . 

. . . no.. 

. . .. 52,630 

2. 

. 90 . 

... 131. 

. . . . 66,370 

I. 


• .. 156. 

. . . . 83,690 

O. 

. 127. 

... 185. 

.... 105,500 

oo. 

. 150. 


• ... i33,ioo 

ooo. 

. 177 . 


. . . . 167,800 

oooo. 

. 210. 


. ... 211, 600 

Circular Mils. 




200,000. 




300,000. 




400,000. 

. 330 . 



500,000. 

. 390 . 

... 590 


600,000. 

. 450 . 

... 680 


- 700,000. 

. 500. 



800,000. 

. 550 . 

... 840 


900,000. 




1,000,000. 

. 650. 



1,100,000. 


. . .1,080 


1,200,000. 

. 730 . 

. . .1,150 


1,300,000. 

. 770 . 



1,400,000. 


. . .1,290 


r, 500,000. 


. . .1,360 


1,600,000. 


... 1,430 


1,700,000. 

. 930 . 

.. .1,490 


i,8oo,oco. 


• . . 1,550 


1,900,000. 




2,000,000. 

..1,050. 

.. .1,670 



The lower 1 imit is specified for rubber-covered wires 
to prevent gradual deterioration of the high insula¬ 
tions by the heat of the wires, but not from fear of 
igniting the insulation. The question of drop is not 
taken into consideration in the above tables. 
























































































s. 

XX) 

lUO 

00 

0 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

28 

27 

28 

29 

30 

31 

32 

33 

34 

35 

36 

37 

38 

39 

40 


ELECTRICITY FOR ENGINEERS 


39 


TABLE OF DIMENSIONS OF PURE COPPER WIRE.* 


Area. 


Diam. 

Mils. 


Circular 

Mils. 

Square 

Mils. 

460.000 

211600.0 

166190.2 

409.640 

167805.0 

131793.7 

364.800 

133079 0 

104520.0 

324.950 

105592.5 

8-932.2 

289.300 

83694.5 

65733.5 

257.630 

66373.2 

52129.4 

229.420 

52633.5 

41338.3 

204.310 

41742.6 

32784.5 

181.940 

33102 2 

25998.4 

162.020 

26250.5 

20617.1 

144.280 

20816.7 

16349.4 

128.490 

16509.7 

12966.7 

114.430 

1 094.2 

10284.2 

101.890 

10381.6 

8153.67 

90.742 

8234.11 

6467.06 

80.808 

6529.94 

5128.60 

71.961 

5178.39 

4067.07 

64.084 

4106.76 

3225.44 

57 068 

3256.76 

2557.85 

50.820 

2582.67 

2028.43 

45.257 

2048.20 

1608.65 

40.303 

1624.33 

1*75.75 

35.890 

1288.09 

1011.66 

31.961 

1021.44 

802.24 

28.462 

810.09 

636.24 

25.347 

642.47 

504.60 

22.571 

509.45 

400.12 

20.100 

404.01 

317.31 

17.900 

320.41 

251.65 

15.940 

254.08 

199.56 

14.195 

201.50 

158.26 

12.641 

159.80 

125.50 

11.257 

126.72 

99.526 

10.025 

100.50 

78.933 

8.928 

79.71 

62.603 

7.950 

63.20 

49.639 

7.080 

50.13 

39.369 

6.304 

39.74 

31.212 

5.614 

31.52 

24.153 

5.000 

25.00 

19.635 

4.453 

19.83 

15.574 

3.965 

15.72 

12.347 

3.531 

12.47 

9.7923 

3.144 

9.88 

7.7635 


Weight and Length. 
Sp. Gr. 8.9. 


Lbs. 

per 

lOOu feet. 

Lbs. 

per 

Mile. 

Feet 

per 

Pound. 

640.73 

3383.04 

1.56 

508.12 

2082.85 

1.97 

402.97 

2127.66 

2.48 

319.74 

1688.20 

3.13 

253.43 

1338.10 

3.95 

200.98 

1061.17 

4.98 

159.38 

841.50 

6 28 

126.40 

667.38 

7.91 

100.23 

529.23 

9.98 

79.49 

419.69 

12.58 

63.03 

332.82 

15.86 

49.99 

263.96 

20.00 

39.65 

209.35 

25.22 

31.44 

165.98 

31.81 

24.93 

137.65 

40.11 

19.77 

104.40 

50.58 

15.68 

82.792 

63.78 

12.44 

65.658 

80.42 

9.86 

52.069 

101.40 

7.82 

41.292 

127.87 

6.20 

32.746 

161.24 

4.92 

25.970 

203.31 

3.90 

20.594; 

256.39 

3.09 

16.331 

323.32 

2.45 

12.952! 

407.67 

1.95 

10.272 

514.03 

1.54 

8.1450 

648.25 

1.22 

6.4593 

817.43 

.97 

5.1227 

1030.71 

.77 

4.0623 

1299.77 

.61 

3.2915 

1638.97 

.48 

2.5548 

2066.71 

.38 

2.0260 

2606.13 

.30 

1.6068 

3286.04 

.24 

1.2744 

4143.18 

.19 

1.0105 

5225.26 

.15 

.8015 

6588.33 

.12 

.6354 

8310.17 

.10 

.5039 

104.8.46 

.08 

.3997 

13209.98 

.06 

.3170 

16654.70 

.05 

.2513 

21006.00 

.04 

.1993 

26487.84 

.03 

.1580 

33410.05 


iile pure copper wire 
1-10 in. diam. 


13.59 ohms at 15.5° C. or 
59.9* F. 


1 circular mil is .7854 square mil. 





















CHAPTER III 



Current Generation in Dynamos — Dynamos — Brushes and 

Commutators. 

Current Generation in Dynamos. If we take a coil of 
wire, Fig. 15, and rapidly thrust a magnet into it, we 
shall observe a certain deflection of the galvano¬ 
meter needle shown with it. This deflection con¬ 
tinues only while the magnet is in motion. After 



we have inserted the magnet and it has come to 
rest the galvanometer needle will return to its normal 
position. When we withdraw the magnet the deflec¬ 
tion of the needle will be in the opposite direc¬ 
tion. If the magnet is inserted or withdrawn with 
a very quick motion, the deflection will be consider¬ 
able. If the magnet is very slowly inserted or with¬ 
drawn the deflection will hardly be noticeable. The 

40 

























ELECTRICITY FOR ENGINEERS 


41 


same phenomena will occur if instead of moving the 
magnet, we hold it stationary and move the coil, or if 
both of them be moved towards or from each other. 
The deflection of the compass needle indicates that a 
current of electricity is passing along the wire, and the 
experiments above described show exactly how cur¬ 
rents of electricity are produced in dynamos. 

An electromotive force is induced by rapidly cutting 
“lines of force,” that is, by moving either a magnet 
over a wire or a wire over or near a magnet. The 



figure 16. 


current in turn is the result of this electromotive force 
acting in a closed circuit. A bar of iron becomes an 
electromagnet if we wind about it a few turns of wire 
and cause a current of electricity to flow along the 
wire, Fig. 16. The magnetism is conceived to consist 
of lines of force, which leave the bar at one end and 
enter it at the other, the direction of these lines 
depending upon the direction in which the current 
circulates about the bar of iron. The number of these 
lines of force depends upon the number of ampere 
turns in the iron bar and on the diameter, length and 
quality of the iron bar. 



















42 


ELECTRICITY FOR ENGINEERS 


Ampere turns is a term used to indicate the mag¬ 
netizing force; it is the number of turns of wire on a 
magnet multiplied by the current in amperes flowing 
through these turns of wire. 

Haskins, in Electricity Made Simple , explains this 
thus: “If, for instance, we have a current of one 

ampere flowing through a single turn of wire around a 
bar of soft iron and we have developed enough mag¬ 
netism to lift a keeper or other piece of iron, weighing 
one ounce, then with one-half the amount of current 
and two coils around the bar, we would obtain the 
same result, and with three turns of wire we would 
require but one-third the current to develop the same 
lifting power in the bar or magnet.” 

The law of magnetic flow is very much the same as - 
the law of current flow. If the iron bar is of low mag¬ 
netic resistance, the flow will be quite great; if of high 
resistance, the flow will be small. 

Lines of force can also be shunted just as a current 
of electricity can; that is, they will follow the path of 
lowest resistance just as a stream of water or a current 
of electricity will. 

Now let us consider the elementary sketch of a 
dynamo, Fig. 17. The wire a represents the armature 
and we have also the iron bar and the coil of wire 
wound on it and, for the present, we may consider the 
battery B as the source of the current which produces 
the magnetism or lines of force in the iron bar. The 
battery current magnetizes the iron bar (which in 
dynamos is known as the field magnet) and produces 
the lines of force indicated by arrows. 

These lines of force leave the field magnet of our 
dynamo at the north pole marked N, and pass through 
the air-gap and armature into the south pole marked S. 


ELECTRICITY FOR ENGINEERS 43 

As we begin to move the wire or armature, it cuts 
through these lines of force and begins to generate an 
electromotive force, which in turn will cause the cur¬ 
rent to flow if the circuit is closed through a lamp or 
other device. 

This current reverses in direction as the wire a passes 
from the influence of the south pole into that of the 
north pole and the brushes B' and B", which transmit 


i 

i 



the current to the outside wires, are so set that they 
change the connection of the wire a at the time that it 
passes from one pole to the other. By this means the 
current in the external circuit is kept constant in 
direction, although it alternates in the armature. 

The faster we turn our wire or armature, the greater 
will be the electromotive force generated. Instead of 
using only one wire, as in Fig. 17, we may take many 

























44 


ELECTRICITY FOR ENGINEERS 


turns before bringing the end out, and in so doing 
obtain the well known drum armature, or, by a slightly 
different method of winding, the gramme ring arma¬ 
ture, Fig. 18. Here we have many wires cutting the 
lines of force at once and our electromotive force with 
the same number of revolutions of the armature is cor¬ 
respondingly increased, and the more turns of wire we 
arrange to cut those lines of force per second the 
greater will be our E. M. F. Instead of providing 



figure 18 . 


more wire or increasing the speed of our armature we 
can increase the magnetism, or number of lines of force, 
by sending more current through the fields, that is 
increasing the “ampere turns.’ * 

If we wish to reverse the current flow we can do so 
by revolving the armature in the opposite direction, 
or by reversing the current through the fields. 

Dynamos. Having so far considered the generation 
of currents in dynamos, we may now consider different 
types of dynamos and their uses. Fig. 19 shows adia- 

















ELECTRICITY FOR ENGINEERS 


4 5 


gram of the wires and connections of a series dynamo. 
The principal use of this dynamo at present is in con¬ 
nection with series arc circuits. (See Fig. 7.) This 
dynamo is usually equipped with an automatic regu¬ 
lator (which will be explained later) to raise or lower 
the voltage as the number of lamps increases or 



decreases, the current remaining constant at about 10 
amperes. By reference to the figure, we can trace the 
current as it flows from the + brush, in the direction of 
the arrows, around both field magnets and through the 
lamps, returning to the - brush on the dynamo. In 
our elementary sketch of a dynamo we used battery 
current to magnetize our fields; we need not consider 









































46 


ELECTRICITY FOR ENGINEERS 


that any more, for in practice all direct current 
dynamos produce their own magnetism by circulating 
some or all of their current through the field coils. 

In the shunt wound dynamo, Fig. 20, the wire in the 
field winding is of such size and connected in such a 
manner as to have a resistance so high that only a 



portion of the main generated current of electricky 
passes around the field magnets. The quantity of cur¬ 
rent passing around these field magnets is also regu¬ 
lated by a resistance sometimes called a rheostat shown 
at R. The resistance to the flow of current through 
this box is adjusted by hand by the attendant and the 
flow of current through this rheostat and around the 












































































ELECTRICITY FOR ENGINEERS 


4 ?'' 


field magnet is what determines the electromotive force 
of the dynamo. 

This type of dynamo is used for electric lighting and 
for operating motors. The electromotive force of such 
a dynamo remains nearly constant, but the current 
varies with the number of lights or motors used. If it 
were connected to too many lights it would deliver too 
much current and become overheated and perhaps 
burn out. The current leaves at the + brush, passes 
through whatever lamps happen to be switched on and 
returns to the — brush. 

Fig. 21 shows a diagram of a compound wound 
dynamo. This is really a combination of the series 
and shunt dynamos. If the current in a series dynamo 
is not kept constant the magnetism in the fields will 
vary as the current varies, and consequently its volt¬ 
age will be very unsteady. This makes such a dynamo 
unfit for use with variable currents. 

The voltage of a shunt dynamo is quite constant with 
variable loads, but still it leaves much room for 
improvement; not because of any variation in the 
induced electromotive force, but because of the losses 
occurring in the armature and wires conveying current. 
The loss of voltage in the armature and line equals the 
current multiplied by the resistance; consequently, as 
the current increases more and more volts are lost and 
the pressure goes down. If we would have the pressure 
remain at its normal value, we must find some way to 
increase the field magnetism as the current delivered 
by the dynamo increases, and this is the purpose of 
the compound winding. The compound winding car¬ 
ries the total current of the dynamo around the fields, 
but only a few times, just often enough so that the 
increase in magnetism resulting from this current may 


48 


ELECTRICITY FOR ENGINEERS 


make up for the loss in the armature or line. Dyna¬ 
mos may be compounded for any per cent, of loss 
desired. 

The foregoing descriptions are those of direct cur¬ 
rent dynamos, and they are called direct or continuous 




FIGURE 


21 . 



current dynamos because the current flow continues in 
one direction out of the positive or + side of the 
dynamo, to the external circuit, and back again to the 
negative or — side of the dynamo. The current as it 
is generated in the coils of the armature which 















































































ELECTRICITY FOR ENGINEERS 


40 


revolves between the field or pole pieces, is alter¬ 
nating; that is to say, if the armature wires were con¬ 
nected to collector rings the current in the outside 
wires would be reversed every time the position of the 
wire in the armature were changed from the influence 
of one pole piece to that of the other. If the coils 
constituting the armature are connected to a device 
called the commutator, they will be commutated or 
rectified. 

Such a commutator is formed of alternate sections of 
conducting and non-conducting material, running 
parallel with the shaft with which it turns. It is 



figure 22. 


placed on the shaft of the armature so that it rotates 
with it, as shown in Fig. 22. The brushes press upon 
its surface and collect the current from the bars. (See 
Fig. 31.) The function of the commutator is to change 
the connections of the armature coils from the + or 
positive to the negative or — side of the circuit at the 
time at which the coil connected to the bar under the 
brush passes from the influence of one pole piece into 
that of the other. This is the time at which the cur¬ 
rent in the coil reverses in direction, and is called the 
neutral point. If we consider, for the sake of simplic¬ 
ity, an armature having only one turn of wire on it, 
as Fig. 17, there will be a time while the coil is in the 



















50 


ELECTRICITY FOR ENGINEERS 


position indicated by dotted lines at c and d when no 
current is being generated. The brushes on any 
dynamo should always be set at this point, for this is 
the point of least sparking. In actual practice all 
commutators have quite a number of bars and it is 
impossible to avoid, in passing under the brushes, that 
at least two of them are in contact with a brush at the 
same time. If a brush did leave one bar before it 
touches another, the current would be entirely broken 
for that length of time and much sparking would 
result. The nature of all armature windings is such 
that while the brush is in contact with the commutator 
bars it short circuits that coil between them. This is 
the main reason why the brushes must be kept at a 
point at which the coil which is short circuited gener¬ 
ates no current. 

Although the electromotive force generated in one 
coil of a dynamo is very small, the resistance of the 
“short circuit” formed by the dynamo brush is also 
very small and therefore the current may be quite large. 
This current is the main cause of sparking in dynamos. 
The number of bars constituting a commutator depends 
upon the winding of the armature, and the number of 
coils grouped thereon. By increasing the number of 
coils and commutator sections the tendency to spark 
at the brushes is decreased, and the fluctuations of the 
current are also decreased. However, there are many 
reasons against making the number of bars on a com¬ 
mutator very great. Increasing the number of bars in 
a commutator increases the cost of manufacture, and 
in smaller dynamos if the number of bars be increased 
beyond a certain extent, each bar becomes so thin 
that a brush of the proper thickness to collect the cur¬ 
rent from the commutator would lap over too many 


ELECTRICITY FOR ENGINEERS 


51 


bars of the commutator at one time. Each commu¬ 
tator bar should be of the size that will present suffi¬ 
cient metal for the carrying capacity of the current 
generated in the coil to which it is connected. Differ¬ 
ent builders of dynamos have different ideas as to the 
number of amperes that may be carried per square inch 
in a commutator bar, but where a commutator is made 



of 95 per cent, copper it is usual to allow for each ioo 
amperes a commutator bar surface of \y 2 sq. in. 

The method of electrical connection between the 
commutator bar and the coil of the armature varies in 
different designs. Some builders solder the terminals 
of the coils to the commutator bars; others bolt the 
terminals of the coils to the bars; and some makers 
use hard drawn copper and “form” the armature coil 
in such a manner that both ends of the coil become 


52 


ELECTRICITY FOR ENGINEERS 




commutator bars, making the coil continuous from one 
end of the commutator bar to the end of the diametric¬ 
ally opposite commutator bar. 

In Fig. 23 vve show a so-called “formed” armature 
coil, after it has been prepared by properly insulating 
it and bending it into shape ready to be applied to the 
laminated armature body. 

In Fig. 24 is shown a “formed” coil armature with 


figure 25 . 

nated armature body keyed on to the shaft ready to be 
wound. 


figure 24 . 


the winding almost finished. The commutator is yet 
to be placed on the shaft and the coil terminals con¬ 
nected to the commutator bars. 

In Fig. 25 we have an armature shaft with the lami- 










ELECTRICITY FOR ENGINEERS 


53 


The body on which the armature coils are to be 
wound is made up of sheet iron punchings and placed 
on the armature shaft in the same manner that you 
would put ordinary iron washers on a lead pencil. 
These punchings or discs are insulated from one 
another by having previously been painted with a coat 
of shellac; for there is the same tendency to produce 
current in the iron part of the armature, due to the 
cutting of the magnetic lines, as there is in the copper 
wire which is wound on its surface. If the iron core 
were solid, there would be a very large current circu¬ 
lating in the same direction as that which flows through 
the wires. Such a current would be entirely useless 
and would heat the armature; to prevent this the 
armature is built up of thin sheet iron discs. 

Brushes and Commutators. Figs. 26 to 30 show differ¬ 
ent arrangements of modern brushes and brush-holders. 
These are used to take the current from the commu¬ 
tator and deliver it to the outside wires in the case of a 
dynamo, and for the opposite in the case of a motor. 

There are many different designs and constructions 
of brushes and brush-holders, and these designs are 
brought about by the various ideas of different builders 
in their attempt to produce various advantageous 
results, but the electrical connections and underlying 
principles remain the same whether a copper or a car¬ 
bon brush be used. 

In any construction of brush holding device, if great 
care is not exercised in keeping it thoroughly clean, 
trouble is sure to be the result, and trouble of this 
nature increases so rapidly that unless the attendant 
immediately sets about to right it, a burned out arma¬ 
ture is almost sure to be the consequence sooner or 
later. In alternating current dynamos, where brushes 


54 


ELECTRICITY FOR ENGINEERS 


rest on collector rings instead of commutators, it is 
much easier to keep out of trouble, because the 
brushes in this case merely collect the current from 
the rings and do not commutate or rectify it. 

The brushes and commutator of a dynamo or motor 



figure 26 . 


are probably the most important parts with which the 
engineer has to deal. Great care should be taken that 
the brushes set squarely on the commutator and that 
the surface of the brushes and commutator are as 
smooth as possible. It is a good plan, and in some 





ELECTRICITY FOR ENGINEERS 


55 


cases the brush-holders are so made, that the brushes 
set in a staggering position, that is to say, in a posi¬ 
tion so that all the brushes will not wear in the same 
place over the circumference of the commutator and 



cause uneven wear across the length of the commutator 
bars. In most machines the armature bearing is left 
so that there is more or less side motion, which, when 
the armature is running, causes a constant changing of 
the position of the brushes and commutator. 








56 


ELECTRICITY FOR ENGINEERS 



Whatever style of brush is used, the commutator 
should be kept clean and allowed to polish or glaze 
itself while running. No oil is necessary unless the 
brushes cut, and then only at the point of cutting. A 
cloth (not cotton waste) slightly greased with vaseline 
and applied to the surface of the commutator while 


FIGURE 28 . 

running is best for the purpose of preventing the com¬ 
mutator from cutting. Should the commutator 
become rough, it should be smoothed with sandpaper, 
never using emery cloth, because emery cloth is con¬ 
ductor of electricity, and the particles of emery are 
liable to lodge, themselves between the commutator 
bars in the mica and short circuit the two bars, thereby 







ELECTRICITY FOR ENGINEERS 


57 


burning a small hole wherever such a particle of emery 
has lodged itself. The emery will also work into the 
brushes and copper bars and wear them down; it being 
almost impossible to remove all the emery. 

In the end-on carbon brushes, Fig. 30, the contact 
surface of the brushes should be occasionally cleaned 
by taking a strip of sandpaper, with the smooth side 
of the paper to the commutator, and the sanded side 
toward the contact surface of the brush, and then by 



FIGURE 29 . 


leaving the tension of the brush down on the sand¬ 
paper, it is an easy matter to move the sandpaper to 
and fro and throughly clean off the glazed and dirty 
surface from the carbon, leaving it with a concave that 
will exactly fit the commutator. 

The advantages of carbon brushes are many. 
Among the cardinal points are: The armature may 
run in either direction without it being necessary to 
alter the brushes; the carbon can be manufactured with 
a quantity of graphite in its construction, thereby 









58 


ELECTRICITY FOR ENGINEERS 


lowering the mechanical friction of the brushes on the 
commutator; they do not cut a commutator so much 
by sparking; the commutator has a longer life, the 
wear being more evenly distributed. 

Carbon brushes, due to their rather high resistance, 
will often heat up considerably, but, although this 
heat is objectionable, their resistance tends to cut 
down the sparking. The brushes are sometimes coated 
with copper to reduce their resistance. Often a car- 



FIGURE 30 . 


bon brush will be found which is very hard. As a rule 
such a brush should be thrown away, as it will heat 
abnormally and at the same time wear the commu¬ 
tator. 

In Fig. 31 we have one of the various so-called old 
styles of leaf brush-holders. The encl-on brushes are 
more generally used in modern practice, because their 
contact surface area is not increased or decreased bv 
wear. Consequently the brushes always remain in a 
diametrically opposite position. With the old style 



ELECTRICITY FOR ENGINEERS 


59 


brush-holding device, where the brushes rest on the 
commutator at a tangent, great care should be exer- 



A / 


FIGURE 31 . 

cised not to allow the brushes to wear in a position so 
that their points will be out of diametrical opposition. 


/ 

' B 

/ M 



In Fig. 31 we show the correct way that this type of 
brush should be set, 






















CO ELECTRICITY FOR ENGINEERS 

In Figs. 32 and 33 we show the incorrect way. 

By remembering that each one of the commutator 
bars is the end of a coil, and then just mentally tracing 
the current through the coils from one brush to the 
other, we can readily understand'what the results are 
when the brushes are neglected and left in a relative 
position, as shown in these figures. 

Sparking is the usual result of brushes allowed to 
wear to such an extent. Overloading of a dynamo or 
motor will also cause serious sparking, and no amount 


/ 



FIGURE 33 . 

/ 

of care can prevent damage to armature, commutator 
or brushes, if a machine is permitted to be overloaded. 

Sometimes the commutator will contain one or more 
bars which, as the commutator gets old and wears 
down, will wear away either too fast or too slow, due 
to the metal being harder or softer than the rest of the 
bars forming the commutator. This causes a rough¬ 
ness of the commutator and results in the flashing of 
the brushes and heating of both the commutator and 
brushes. About the only satisfactory method of 










ELECTRICITY FOR ENGINEERS 


61 


remedying this evil is to take out the armature and 
have the commutator turned down in a lathe. 

A short-circuited coil in the armature, or a broken 
armature connection, will also cause considerable 
sparking. Either of these conditions can be located 
by means of a Wheatsone bridge or by what is known 
as the fall of potential method. To make a test with 
this latter method, connect in series with the armature 
to be tested some resistance capable of carrying the 
necessary current, also an ammeter. Some apparatus 
for varying the current strength, such as a water rheo¬ 



stat or lamp rack, must be connected in the circuit, a 
diagram of which is shown in Fig. 34. 

In the diagram, WR is the water rheostat or lamp 
rack, R the known resistance, A the ammeter and M 
the armature to be tested. By means of the water 
rheostat regulate the current passing over the appa¬ 
ratus until it is of such strength that a deflection can 
be obtained on a voltmeter when it is connected to two 
adjacent bars on the commutator. Suppose the arma¬ 
ture coil between bar 1 and 2 on the commutator were 
broken. The voltmeter connected across these two 
bars would give the same reading as when connected 
















62 


ELECTRICITY FOR ENGINEERS 


across the two points 10 and 11. If the voltmeter were 
connected between any other two points on the com¬ 
mutator on the same side as the broken coil no deflec¬ 
tion would be obtained, while connecting the voltmeter 
between any two adjacent bars on the other side of the 
commutator would give practically the same reading 
irrespective of which bars were used. The resistance 
of one or more sections of the armature winding could 
also be found by using Ohm’s law, R = E/C, or the 
resistance would be equal to the voltage divided by the 
current as shown on the ammeter. It must be remem¬ 
bered that this latter will be true only when there is an 
open coil in one side of the armature, for in this case 
only will the whole current flow through the one side. 
If the coil between bars I and 2 were short circuited, 
the voltmeter would show practically no reading 
between these bars; while between any other bars some 
. deflection would be obtained. An open circuit or 
short circuit will nearly always be found by examina¬ 
tion, as the trouble usually happens very close to the 
commutator connections in the case of an open circuit 
and may very often be found between the commutator 
bars themselves, in the case of a short circuit. If the 
trouble is not at these places it will usually be in the 
windings, in which case the only remedy is to have it 
re-wound. Temporary repairs may be made in the case 
of an open circuit by short circuiting the commutator 
bars around the open circuit, but this method should 
only be used in emergency, as the sparking will in time 
destroy the commutator. 

With many dynamos, especially of older types, it is 
necessary to shift the brushes with every change of 
load. The current produced by the armature makes a 
magnet out of it and the magnetism of the armature 


ELECTRICITY FOR ENGINEERS 


63 


opposes that of the fields. In Fig. 35 the armature is 
working with a very light load and the lines of force 
of the field magnets are only slightly opposed by those 



of the armature. In Fig. 36 we assume a heavy load 
on the dynamo and consequently the magnetism of the 
armature opposes that of the fields. This changes the 
location of the neutral point (when the coils under the 
brush generate no current) and it becomes necessary to 



figure 36 . 


shift the brushes accordingly, or great sparking would 
result. The amount of shifting necessary with changes 
of load varies in different dynamos. If the field is 



































64 


ELECTRICITY FOR ENGINEERS 


very strong compared to the armature, it will be but 
little. If the armature (as in some arc dynamos) is 
very strong compared to the field, it will be consider¬ 
able. 

In dynamos, with increasing load, the brushes should 
be shifted in the direction of rotation and in the oppo¬ 
site direction when the load decreases. 

Never allow a dynamo or motor to stand in a damp 
place uncovered. Moisture is apt to soak into the 
windings and cause a short circuit or ground when 
started. Great care should also be used should it ever 
be found necessary to use water on a heated bearing. 
If the water is allowed to reach the armature or com¬ 
mutator, it is bound to cause trouble. Water should 
only be used in case of emergency, and then sparingly. 


CHAPTER IV 


OPERATION OF DYNAMOS 

Constant Potential Dynamos. In order to thoroughly 
explain the operation of dynamos, let us assume that 
we have the task of starting a new shunt dynamo, one 
that has never generated any current. Our first step is 
to open the main switch and turn the rheostat or field 



figure 37 . 


resistance box so that all the resistance is in circuit. 
A rheostat consists of a number of resistances, Fig. 37, 
so arranged that they can be cut in or out of the circuit 
without opening the circuit. By reference to the figure 
it will be seen that the current enters at the handle and 
from there passes to the contact point upon which the 

65 












































































































66 


ELECTRICITY FOR ENGINEERS 


handle happens to rest. If the handle is at I the cur¬ 
rent must pass through all the wire in the box; if it is 
at 2 it simply passes through the handle and out. 

Rheostats for the shunt circuit of a dynamo should 
have sufficient resistance, so that when it is all inserted 
the voltage of the dynamo will slowly sink to zero. 
This method of stopping the action of a dynamo is 



figure 37 . 


perfectly safe and should be followed wherever pos¬ 
sible. 

We are now running our dynamo with all resistance 
in the shunt circuit. This is simply as an extra pre¬ 
caution because we know nothing about this particular 
dynamo. When it is known that the dynamo is in 
good order, the engineer or attendant usually cuts out 
all the resistance, and as the generator builds up or, in 
other words, generates current, he proceeds, by the aid 
of the resistance box, to cut down or diminish the flow 
of electricity around the field magnets of the dynamo, 








ELECTRICITY FOR ENGINEERS 


67 


and thereby diminish the magnetic density of the 
field magnets and the electromotive force of the 
dynamo. 

We must now gradually turn our rheostat so as to 
cut out resistance and watch the voltmeter, which is 
connected as shown at V in Fig. 20, and receives cur¬ 
rent whenever the dynamo is operating. Suppose that 
the voltmeter indicates nothing, and we find that the 
dynamo will not generate. On examination of all the 
connections we find everything correct, and we now 
discover that the dynamo field magnets do not contain 
what is termed “residual magnetism” sufficient to start 
the process of generating current. 

Before an armature can generate current it must cut 
lines of force, that is, it must revolve in a magnetic 
field. If the dynamo has been generating current it is 
likely that the iron cores of the field magnets will 
retain sufficient magnetism to start the generation of 
current again. This magnetism which remains in the 
iron is known as residual magnetism. It will make 
itself manifest by attracting the needle of a compass, 
or if strong, a screw driver or a pair of pliers. If we 
find no magnetism in the iron core of the field mag¬ 
nets, we may take the ends of the shunt winding on the 
field magnets and pass current over them from a bat¬ 
tery. This current will produce sufficient magnetism 
to cause the generator to build up; in other words, if 
we disconnect these batteries, and connect the wires 
back again from where we got them, we will find that 
we can generate current with the machine. 

When the machine begins to generate, we watch the 
voltmeter and cut resistance in or out of the circuit 
according whether we need to lower or raise the volt¬ 
age. If we have only one dynamo we may close the 


68 


ELECTRICITY FOR ENGINEERS 


main switch before we begin generating or after we 
have attained full voltage. 

Again referring to the pole pieces on the dynamo, it 
is possible that there is a sufficient quantity of residual 
magnetism in the pole pieces, and that the polarity of 
both field magnets, between which the armature is 
revolving, is the same. This would also cause the 
dynamo to fail in generating current. If sending bat¬ 
tery current through the coils does not make one field 
a north pole and the other a south pole, one of the 
fields must be connected wrong, and we must make 
some changes in the connection. 

Referring to Fig. 20, a and b are the terminals of the 
shunt winding on the fields. If the winding of the 
fields is correctly put on it will be as in the little sketch 
at lower corner; that is, if both field magnets were 
taken out of their places and put together, the wind¬ 
ing should run as one continuous spool. But if the 
winding on one field is wrong, we need simply change 
its connection, as, for instance, transferring c to a and 
a to c. 

In order that a dynamo may excite itself, it is neces¬ 
sary that the current produced by the residual magnet¬ 
ism shall flow in such a direction as to strengthen this 
residual magnetism. If the current produced by the 
residual magnetism flows through the field coils in the 
opposite direction this will tend to weaken the residual 
magnetism and consequently to reduce the current 
which flows. 

For this reason if the first attempt to start a dynamo 
with battery current fails, the battery should be applied 
with the opposite poles so that the magnetism it pro¬ 
duces in the fields will be in the opposite direction. 

The magnetism, the fields, and all parts of the 


ELECTRICITY FOR ENGINEERS 


69 


dynamo may be in perfect working order and yet a 
short circuit in any part of the wiring will prevent 
the dynamo from building up This short circuit 
will furnish a path of such low resistance that all cur¬ 
rent will flow through it and none can flow through the 
fields to induce magnetism. Often dynamos fail to 
generate because of broken wires in the field coils, 
poor contacts at brushes, or loose connections. Some¬ 
times also part of the wiring may be grounded on 
the metal parts of the dynamo frame. A faulty posi¬ 
tion of the brushes may also be a cause for the machine 
not generating. In some machines the proper position 
for the brushes is opposite the space between the pole 
pieces, while in other machines their proper position is 
about opposite the middle of the pole piece. If the 
exact position is not known, a movement of the brushes 
will sometimes cause the generator to build up. 

If there are several dynamos to be started great care 
must be taken to see that the second machine is oper¬ 
ating at full voltage before the switch is closed con¬ 
necting it to the switch board. The voltage should be 
exactly the same as that of the first machine and the 
rheostat worked to keep it so. If it is less, it is pos¬ 
sible that the first machine will run the second as a 
motor; if it is more, the second machine may run the 
first as motor, the machine having the higher voltage 
will always supply the most current. 

It is also necessary before throwing in the second 
machine (connecting it to the switch board) to see that 
its polarity is the same as that of the machine with 
which it is to run. By reference to Fig. 38 it will be 
seen that the + poles of both machines connect to the 
same bar, and if one of these machines is running and 
we wish to connect the other with it, we must first be 


70 


ELECTRICITY FOR ENGINEERS 


sure that the wire of the second machine which leads 
to the top bus-bar is of the same polarity. That is, if 
the top bus-bar is positive, or sends out current, the 
wire of all dynamos connected to it must also be posi¬ 
tive. The simplest way to find the positive pole of a 
dynamo is with a cup of water. Take two small wires 
and connect one to each of the main wires of the 
dynamo and then insert the bare ends of both wires 
into the water, small bubbles will soon be seen to rise 
in the water from one of the wires. That wire which 
gives off the bubbles is the negative wire. Take care 
that in making this test you do not get the ends of the 
small wires together or against the metal of the cup or 
you will form a short circuit. The polarity of both 
dynamos must be tested and wires of same polarity 
connected to the same bus-bar. 

Where several machines are to be operated in paral¬ 
lel, compound dynamos are generally used, because it 
is troublesome to keep two shunt machines working in 
harmony. 

The starting of a compound wound dynamo is the 
same as that of a plain shunt dynamo, but in connect¬ 
ing a compound wound dynamo to its circuit it is 
necessary to be sure that the shunt coils and series coils 
tend to drive the lines of force around the magnetic cir¬ 
cuit in the same direction. If the series coil is con¬ 
nected up in the opposite direction to the shunt coil 
the dynamo will build up all right and will work satis¬ 
factorily on very light loads. When, however, the 
load becomes even, five or ten per cent, of full load, 
the voltage drops off very rapidly and it is impossible 
to get full voltage with even half the load on. This is 
because the ampere turns due to the series coils 
decrease the total ampere turns acting on the magnetic 


ELECTRICITY FOR ENGINEERS 


71 


circuit instead of increasing them as the load comes 
on. This lowers the magnetic flux and of course 
lowers the resulting voltage. In such a case it will be 
necessary to reverse either the field or series coils. 

Fig. 38 and the following description of compound 
dynamos and their connections is taken from Wiring 
Diagrams and Descriptions , by Horstmann and Tousley, 
published by Frederick J. Drake & Co., Chicago. 



figure 38 , 


Fig. 38 shows connections for two compound wound 
dynamos run in parallel. When two or more com¬ 
pound wound dynamos are to be run together, the 
series fields of all the machines are connected together 
in parallel by means of wire leads or bus-bars which 
connect together the brushes from which the series 
fields are taken. This is known as the equalizer, and 
is shown by the line running to the middle pole of the 
dynamo switch. By tracing out the series circuits it 


































































































n 


ELECTRICITY FOR ENGINEERS 


will be seen that the current from the upper brush of 
either dynamo has two paths to its bus-bar. One of 
these leads through its own fields, and the other, by 
means of the equalizer bar, through the fields of the 
other dynamo. So long as both machines are gener¬ 
ating equally there is no difference of potential between 
the brushes of No. I and No. 2. Should, from any 
cause, the voltage of one machine be lowered, current 
from the other machine would begin to flow through 
its fields and thereby raise the voltage, at the same 
time reducing its own until both are again equal. The 
equalizer may never be called upon to carry much cur¬ 
rent, but to have the machines regulate closely it 
should be of very low resistance. It may also be run 
as shown by the dotted lines, but this will leave all 
the machines alive when any one is generating. The 
ammeters should be connected as shown. If they 
were on the other side they would come under the 
influence of the equalizing current and would indicate 
wrong, either too high or too low. The equalizer 
should be closed at the same time, or preferably a lit¬ 
tle before the mains are closed. In some cases the 
middle, or equalizer, blade of the dynamo switch is 
made longer than the outside to accomplish this. The 
series fields are often regulated by a shunt of variable 
resistance. To insure the best results compound ma¬ 
chines should be run at just the proper speed, other¬ 
wise the proportions between the shunt and series coils 
are disturbed. 

GENERAL RULES 

1. Be sure that the speed of the dynamo is right. 

2. Be sure that all the belts are sufficiently tight. 

3. Be sure that all connections are firm and make good contact. 

4. Keep every part of the machine and dynamo room scrupm 
lously clean. 


ELECTRICITY FOR ENGINEERS 


73 


5. Keep all the insulations free from metal dust or gritty sub¬ 
stances. 

6. Do not allow the insulation of the circuit to become impaired 
in any way. 

7. Keep all bearings of the machine well oiled. 

8. Keep the brushes properly set and see to it that they do not 
cut or scratch the commutator. 

9. If the brushes spark, locate the trouble and rectify it at once. 

10. The durability of the commutator and brushes depends on 
the care exercised by the person in charge of the dynamos. 

11. At intervals the dynamos must be disconnected from the 
circuit and thoroughly tested for leakage and grounds. 

12. In stations running less than twenty-four hours per day, the 
circuit should be thoroughly tested and grounds removed (if any 
are found) before current is turned on. 

13. Before throwing dynamos in circuit with others running in 
multiple, be sure the pressure is the same as that of the circuit; 
then close the switch. 

14. Be sure each dynamo in circuit is so regulated as to have its 
full share of load, and keep it so by use of resistance box. 

15. Keep belting in good order; when several machines are 
operating in parallel and a belt runs off from one, the others will 
run this machine as a motor. 

16. In the same way if you shut down an engine driving a 
generator, the other generators will run the generator and the 
engine. 

Constant Potential Switchboard. In Fig. 39 we show 
the usual type of switchboard employed to connect, 
or switch various dynamos and to feed various circuits 
from. These types, sizes and arrangements of switch¬ 
boards vary and depend entirely on the type and size 
of the plant, the number of dynamos used and the num¬ 
ber of circuits to be controlled. The switchboard in 
this cut has three dynamo panels and one load panel. 
At the left of the board and near the top is the volt¬ 
meter, while on the three left panels are the dynamo 
main switches and their respective amperemeters. On 
the lower part of these three machine panels will be 


74 


ELECTRICITY FOR ENGINEERS 


noticed the protruding hand wheels of the field resist¬ 
ance boxes, which are hidden back of the board. The 
meter at the top of the right hand panel is the load 
amperemeter and registers the total number of amperes 



figure 39 . 

that are being supplied to the circuits whose several 
switches are just below the meter. 

Fig. 40 shows diagrammatically the reverse side of a 
similar switchboard. Below all of the switches there 
are installed fuses in each wire. The object of these 
fuses is to protect the wires and also the dynamos. 
These fuses consist of an alloy which melts at a com- 

























ELECTRICITY FOR ENGINEERS 


75 


paratively low temperature. If, for instance, a short 
circuit occurs in any line, the current will suddenly 
become very great and will generate considerable heat. 
This heat will cause the fuse to melt and open the cir¬ 
cuit. If the fuse did not melt the current would con¬ 
tinue and overheat the wires, causing considerable 



FIGURE 40 . 


damage and perhaps fires. The fuses should always 
be chosen of such a size that they will melt before the 
current rises enough to do any damage. 

Operation of Constant Current Dynamos. Constant cur¬ 
rent dynamos differ from constant potential dynamos 
mainly in the higher voltage for which they are usually 
























































































76 


ELECTRICITY FOR ENGINEERS 


constructed. Such machines are always more or less 
dangerous to life, and great care must be taken not to 
touch any of the current-carrying parts with bare hands. 

When such parts must be handled rubber gloves are 
very convenient and useful if kept dry. High voltage 
machines should always be surrounded by insulating 
platforms of dry wood, or rubber mats, so arranged 
that one must stand on them in order to touch any 
part of the machine. By reference to Fig. 19 it will 
be seen that the constant current dynamo is not 
equipped either with a voltmeter or a field rheostat; 
but an amperemeter should always be used. The 
troubles encountered with these dynamos are much the 
same as those of constant potential dynamos. Most of 
them are referred to in the following descriptions and 
instructions for different systems and to avoid repeti¬ 
tion need not be mentioned here. 

The type of dynamo generally used with constant 
currents is shown in Fig. 19 and is series wound; that 
is, the same current that passes through the lights also 
passes through the fields and excites them. The fields 
of this dynamo are connected with a short circuiting 
switch, S, which is generally used when the machine is 
to be shut down. When this switch is closed it forms 
a path of much lower resistance than do the fields of 
the dynamo and all current passing through it and the 
dynamo loses its magnetism and stops generating. 
A constant potential dynamo will not begin genera¬ 
ting if there is a short circuit anywhere in the wiring 
connected with it, but with the constant current 
dynamo it is often necessary to provide a short circuit 
in order to start it. If there is very much resistance 
in the line or if it is entirely open the dynamo will fail 
to generate. 


ELECTRICITY FOR ENGINEERS 


77 


In order to start generation a small wire may be 
attached to one of the terminals of the dynamo and 
the other end brought in contact with the other ter¬ 
minal for a fraction of a second or the shortest possible 
instant. If the circuit happens to be arranged some¬ 
what as shown in the figure, the plug may be inserted 
so that the dynamo is started through only one lamp. 
When this lamp is burning properly the plugs may be 
suddenly withdrawn and the current will now force 
itself through the other lamps. This process is known 
as “jumping in” and should be used only in an emer¬ 
gency, as much damage may be caused, especially if a 
dynamo is already running a large number of lamps 
and is then “jumped into” a bad circuit. This is also 
often done, but is just as dangerous as it would be to 
attempt to start a heavy steam engine by opening up 
the throttle valve with a quick jerk. 

Constant current dynamos are always equipped with 
automatic regulators and before the dynamo is started 
special attention must be given the regulator to see 
that it is in proper working order. 

Often it may be desirable and even necessary to run 
two dynamos in series, as, for instance, if a circuit has 
been extended beyond the capacity of one machine. 
In such a case the regulator of one machine is cut out 
and that machine set to operate at about its highest 
electromotive force, and the variations are taken care 
of by the other dynamo. 

The Brush System. The brush arc dynamo is quite 
distinct from other constant current dynamos in general 
use. We shall therefore give the following descrip¬ 
tion of it taken from literature furnished by the Gen¬ 
eral Electric Company. 

The brush arc generator is of the open coil type, the 


78 


ELECTRICITY FOR ENGINEERS 


fundamental principle of which is illustrated in Fig. 
41. Two pairs of coils, placed at right angles on an 
iron core, are rotated in a magnetic field. The hori¬ 
zontal coils represented in the diagram are producing 
their maximum electromotive force, while the pair of 
coils at right angles to them is generating practically 
no electromotive force. The brushes are placed on 
the segments of the four-part commutator, so as to col¬ 
lect only the current generated by the two horizontal 



figure 41 . 


coils. The other coils are open circuited or com¬ 
pletely cut out of the circuit. 

Such a machine will generate current, continuous in 
direction, but fluctuating considerably in amount. 
These fluctuations will be diminished by the addition 
of more coils to the armature. 

Fig. 42 shows the connections of an eight-coil brush 
arc generator. Each bobbin is connected in series 
with the one diametrically opposite. The connection 
is not shown on the diagram. It will be noticed that 
of those coils connected to the outer ring on which the 
brushes A and A 1 bear, only 3, 3 1 are in circuit, 1, i 1 







ELECTRICITY FOR ENGINEERS 


79 


being entirely cut out; while on the inside ring all 
coils 2, 2 1 and 4, 4 1 are in circuit, the two pairs being 
parallel; 4, 4 1 are coming into the field of best action; 
in other words, they are approaching that part of the 
field in which there is most rapid change of magnetic 
flux, while 2, 2 1 are approaching that part in which the 
flux is uniform. In 4, 4 1 there is an increasing electro- 



FIGURE 42 . 


motive force being generated, and the current is rising; 
while in 2, 2 1 , the electromotive force is decreasing and 
the current falling. Unless 2, 2 1 were cut out of the 
circuit, a point would soon be reached where the elec¬ 
tromotive force in 2, 2 1 would be zero, and conse¬ 
quently 4, 4 1 would be short circuited through 2, 2 1 . 
Just before this occurs, however, 2, 2 1 have passed from 
under the brush and the small current still flowing 




























80 


ELECTRICITY FOR ENGINEERS 


draws out the spark one sees on the commutator of all 
open coil machines. 

Setting the Brushes. A pressure brush should always 
be used over the under brush in the same holder, as it 
improves the running of the commutator and secures 
better contact on the segment. The combination is 
referred to as the “brush.” The brushes should be 
set about in. from the front side of the brass brush- 
holder. 

In setting the brushes, commence with the inner pair 
and set one brush about 5^ in. from the holder to tip 
of the brush, then rotate the rocker or armature until 



the tip of the brush is exactly in line with the end of a 
copper segment, as shown in Fig. 43. The other 
brush should be set on the corresponding segment 90° 
removed (the same relative position on the next for¬ 
ward segment); but if the length of the brush from the 
holder is less than 5 }£ in., move both brushes forward 
until the length of the shorter brush from the holder 
is 5^ in. Now set the two extreme outer brushes in 
the same manner, clamping firmly in position, and by 
using a straight edge or steel rule, all the brushes can 
be set in exactly the same line and firmly secured. 
The spark on one of the six brushes may be a trifle 




ELECTRICITY FOR ENGINEERS 


81 


longer than on the others. In this case, move the 
brush forward a trifle so as to make the sparks on the 
six brushes about the same length. Equality in 
the spark lengths is not essential, but it gives at a 
glance an indication of the running condition of the 
machine. 

Brushes should not bear on the commutator less than 
}i in. from the point of the brush, or, as illustrated in 
Fig. 44 (a), they will tend to drop into the commu¬ 
tator slots and pound the copper tip of the wood block, 
causing the fingers of the brushes to break off. If, on 
the other hand, the bearing is too far from the end, or 
the brushes are set too long, as in Fig. 44 (b), the 



figure 44a. figure 44b. figure 44c. 


point of the brush will not be in contact with the seg¬ 
ment, thereby prolonging the break, and allowing the 
spark to follow the tip with consequent burning of the 
segments and brushes. 

Fig. 44 (c) shows correct seating with the tip of the 
brush nearly tangential and stiff on the segment as it 
leaves. 

Care of Commutator. If the commutator needs lub¬ 
rication, oil it very sparingly. Once or twice during 
a run is ample. If the oil has a tendency to blacken 
the commutator instead of making it bright, wipe the 
commutator with a dry cloth. Too much oil causes 
flashing. 

The machine, of course, generates high potential, 
and the cloth, or whatever is used to oil the commu- 









82 


ELECTRICITY FOR ENGINEERS 


tator, should therefore be placed on a stick so that the 
hand is not placed in any way between the brushes. 

A rubber mat should be provided for the attendant 
to stand on when working around the commutator or 
brushes. 

One hand only should be used, and great care exer¬ 
cised not to touch two brush clamps or brushes at the 
same time; never with switches closed. 

As soon as current is shut off from the machine the 
commutator should be cleaned. A piece of very fine 
sandpaper held against the commutator under a strip 
of wood for about a minute before the machine is 
stopped, will scour the commutator sufficiently. The 
brushes need not be removed. An effort should be 
made to have the machine cleaned immediately after 
it is shut down. Five minutes at that time will give 
better results than half an hour when the machine is 
cold. Never use a file, emery cloth or crocus, on the 
commutator. New blocks will sometimes cause flash¬ 
ing, due to the presence of sap in the wood. The 
machine should be run for a few hours with a slightly 
longer spark, say y 2 in., and the commutator then 
thoroughly cleaned with fine sandpaper. 

All constant current arc machines require an auto¬ 
matic regulator to increase the voltage as more lamps 
are cut into the circuit and decrease it as lamps are 
cut out. 

We will give only one of the several forms of regu¬ 
lators used with this system. 

The form I regulator is placed on the frame of the 
machine beneath the commutator, and a constant 
motion is imparted to its main shaft through a small 
belt running around the armature shaft. (See Fig. 
46.) By means of magnetic clutches and bevel gears, 


ELECTRICITY FOR ENGINEERS 


83 


a pinion shaft is rotated, which moves the rack and the 
rocker arm and so shifts the brushes on the commu¬ 
tator to maintain a spark of about ^4 in. on short cir- 



\To Control ler 


FIGURE 46 


cuit and }£ in. at full load; at the same time the 
rheostat arm is moved over the contacts to cut 
resistance in or out of the shunt around the field 
circuit. 

































84 


ELECTRICITY FOR ENGINEERS 


The current for the magnetic clutches is regulated by 
the controller. 

The controller consists principally of two magnets 
which are energized by the main current and act when 
the current is too high or too low by sending a small 
current to one of the clutches. 

A careful examination of the controller (see Fig. 
47), in connection with Fig. 46, will give a clear idea 

CONNECTIONS OF BRUSH CONTROLLER 



To Clutch at F for Clockwise. To Clutch at E for Clockwise. 

To Clutch at E for Counter Clockwise. To Clutch at F for Counter Clockwise 

Changed 6 June'90. 


FIGURE 47. 

of its regulating action. It is generally advantageous 
to make the yoke which carries the brushes on the 
machine and the arm moving the rheostat, rather 
tight. As the magnetic clutches act with considerable 
force, it is not necessary to adjust these moving parts 
so loosely that they will move without considerable 
pressure on the rocker handle. Less difficulty will 
then be experienced in adjusting the controller. 













































































ELECTRICITY FOR ENGINEERS 


85 


For shunt lamps, the controller may be adjusted to 
permit a variation of .4 ampere above or below normal; 
for differential lamps, the variation above and below 
normal should not exceed .2 ampere. The limits 
given in the following instructions are for differential 
lamps, and may be extended .2 ampere above or below 
for shunt lamps. 

If the controller is out of adjustment and fails to 
keep the current normal, do not try to adjust the ten- 
ions of both armatures at the same time. For exam¬ 
ple, suppose the current is too high, either one of the 
two spools may be out of adjustment. The left-hand 
spool I may not take hold quickly enough, or the 
spool F may take hold too quickly. To make the 
adjustment, screw up the adjusting button K on the 
right hand spool, increasing the tension. This will 
have a tendency to let the current fall much lower 
before the armature comes in contact with H, to cause 
the current to increase. By simply tapping the arma¬ 
ture G quickly with a pencil or piece of wood, forcing 
it down to its contact, and at the same Time watching 
the ammeter, the current may be brought up to 6.8 
amperes if 6.6 amperes is normal, or to 9.8 if 9.6 
amperes is normal. With the current at 6.8 amperes, 
which is .2 ampere high, the adjusting button L should 
be turned to increase the tension on this spring until 
the armature M comes in contact with contact N, 
which will force current down through O. The clutch 
which pulls the brushes forward and rocks the rheostat 
back for less current will thus be energized. Repeat 
this adjustment two or three times, but do not touch 
the adjusting button K; adjust L until it is just right. 

At the side of the armature M a little wedge is 
screwed in by means of an adjusting button, and 


86 


ELECTRICITY FOR ENGINEERS 


increases or decreases the leverage on this armature. 
See that this wedge is fairly well in between the core 
or frame of the spool and the spring of the armature. 
The armature M may have to be taken out and the 
spring slightly bent. It is advisable to have the screw 
which passes through the adjuster button L about half 
way in, to allow an equal distance up and down for 
adjusting this lighter spring after the wedge shaped 
piece is in the right position to give the necessary 
tension on the spring which is fastened to the arma¬ 
ture M. 

In the right-hand corner P, a small bent piece of 
wire is placed for tightening up the screw which fas¬ 
tens the spring to the frame of the spool. As the con¬ 
tact made by the spring and the frame of the spool 
held together by a screw and button is a part of the 
magnetic circuit, it will be almost impossible to get 
this spring back to exactly the same tension after once 
removing it. Therefore, the adjusting buttons of the 
controller must be turned slightly in order to bring it 
back to its proper adjustment. This, however, is an 
after consideration, and care should be taken to have 
the screw which holds the spring and frame together 
always tight. 

Having adjusted the spool I so that the current will 
not rise above 6.8 amperes (or 9.8 amperes), move the 
armature M up to contact N with a pencil or piece of 
wood, causing the current to be reduced to about 6.2 
(or 9.2). After the current settles at this point, decrease 
the tension on the spring which is fastened to armature 
G, allowing this armature to fall down to contact H. 
Current will then flow through Q, which will rock the 
brushes back and also move the rheostat arm for more 
current. As the spool I has been adjusted for 6.8 (or 


ELECTRICITY FOR ENGINEERS 


87 


9.8) amperes, the current cannot rise above that amount 
no matter how the spool F is adjusted. 

With very little practice in moving the armature of 
one spool with a pencil, the other can be adjusted 
much more readily than if an attempt is made to adjust 
the screws K and L at the same time. 

The two small shunt coils, R and S, are connected 
around the two contacts simply to decrease the spark 
between the silver and platinum contacts. If they 
should become short circuited in any way, so that 
their resistances become diminished, sufficient current 
may pass through either of them to operate the regu¬ 
lator. If unable to locate the trouble disconnect these 
coils at points T and U, when a thorough examination 
can be made. M and G need not move more than just 
enough to open the contact; in. is ample. 

In starting the machine, the lower switch, which 
short circuits the field, should be opened last. 

The switch in the left-hand corner of the controller, 
figure 47 cuts out the two resistance wires which are 
used to force the current through wires O and Q to 
the clutches. Open this switch, which leaves the 
automatic device of the controller in circuit, so that it 
will move the brush rocker. Unclamp the brush rocker 
from the rheostat arm rocker. Move the brushes by 
hand to give the proper spark, allowing the rheostat 
arm, however, to be moved by the controller. After 
the switches are opened, the rheostat arm will go clear 
around to a full load position, and then, as the current 
rises, the controller takes hold and brings the arm 
back. In the meantime, rock the brushes forward or 
backward and keep the spark about the proper length, 
say }i in., at full load to 3 /% in., on short circuit. 
Gradually the rheostat arm will settle, the spark will 


88 


ELECTRICITY FOR ENGINEERS 


become constant, and the machine will give its proper 
current. Then clamp the rocker and rheostat arm 
together and let the machine regulate itself. 

This method is much better than opening the 
switches on the machine and allowing the wall con¬ 
troller to take care of the machine from the start. By 
allowing the controller to start the machine, a trifle 
longer spark is obtained than by the other method, 


PULLEY END COMMUTATOR END 



figure 48. 


unless the machine is run from the beginning on a very 
full load. 

The machine will require a trifle longer spark on 
light load, or on bad circuits, than when running at 
full load. This fact should be borne in mind in wet 
weather, when trouble with grounds is experienced. 

A reliable ammeter should always be connected in 
the circuit of an arc generator, so that the exact cur¬ 
rent may be read at a glance. It should be connected 
into the negative side of the line where the circuit 
leaves the regulator. 






ELECTRICITY FOR ENGINEERS 


89 


The Thomson-Houston System. The Thomson-Hous- 
ton dynamo differs from other arc dynamos principally 
in the nature of its armature winding. This is shown 
in Fig. 48. One end of each of the three coils is con¬ 
nected to a copper ring common to all. The other end 
of each coil terminates at one of the three commutator 
segments. The management and operation of the 
machine will appear from the following instructions 
taken from pamphlets furnished by the General Elec¬ 
tric Company. 



Setting the Cut-out. After the brushes are in position 
the cut-out must be set. This is done by turning the 
commutator on the shaft in the direction of rotation 
(if the commutator is set in position the whole arma¬ 
ture must be revolved) until any two segments are just 
touching the primary brush on that side, as segments A' 
and A'" touch brush B 4 in Fig. 50. 

Under these conditions brush B 1 should be at the 
left-hand edge of upper segment. Then turn commu¬ 
tator until the same two segments are just touching 


90 


ELECTRICITY FOR ENGINEERS 


brush B~, when the end of brush B 3 should just come 
to the right-hand edge of the lower segment. If the 
secondary brush projects beyond the edge of the seg¬ 
ment the regulator arm should be bent down; if it does 
not come to the edge of the segment, the arm should 
be bent up. 

Care must be taken that the regulator armature is 
down on the stop when the cut-out is being set. 
These adjustments by bending regulator arm are 
always made in the factory before testing the machine, 
and should never be made on machines away from the 
factory, unless the regulator arm has been bent by 
accident. If it becomes necessary to make any adjust¬ 
ments they should be made by means of the sliding 
connection attached to the inner yoke. 

Always try the cut-out on both primary brushes. If 
it does not come the same on both, turn one over. If 
the brush-holders are correctly set by the gauge, there 
should be no trouble in getting the cut-out set properly 
after one or two trials*, 

To set the commutator in the proper position on a 
right-hand machine, with a ring armature, find the 
leading wire of No. : J coil. It is the custom in the 
factory to paint this lead red, also to paint a red mark 
on the center band between two groups of coils, 
namely, the last half of No. I coil and the first half of 
No. 3 coil. The first half of a coil is that group from 
which the lead comes. The last half is diametrically 
opposite the first half and the lead wire belonging to 
it is connected with the brass ring on the outside of 
the connection disk on the commutator end. 

In Fig. 51 the first halves of the three coils are rep¬ 
resented, by 1, 2 and 3, and the last halves by 1', 2? 
and 3'. 


ELECTRICITY FOR ENGINEERS 


91 


A narrow piece of tin with sharply pointed ends is 
bent up over the sides of the middle band at the cen¬ 
ter of the red mark so that the points are opposite each 
other. 

When the red mark and red lead have been found, 
turn the armature until the last half of No. I coil has 
wholly disappeared under the left field and until the 
left-hand edge of the first coil to the right of the red 




FIGURE 51. 


mark (No. 3 in Fig. 51) is just in line with the edge of 
the left field. The red lead will then be in position 
shown in Fig 51, and the armature is in proper posi¬ 
tion to set the commutator. 

In the case of the right-hand drum armature the 
leading wire of the first coil should be found. This iead 
may be recognized from the fact that it is more heavily 
insulated than the rest, and is found in the center of 



















92 


ELECTRICITY FOR ENGINEERS 



the outer coil, on the commutator end. With this 
wire turned underneath, rotate the armature forward, 
or counter-clockwise, until the pegs on the right-hand 



figure 53. 





















ELECTRICITY FOR ENGINEERS 


93 


side of this coil just disappear under the left field. 
(See Fig. 52.) 

The position of the red lead and the red mark on the 
band are the same on all armatures, but their positions 
in the fields of the machines called left-hand (clock¬ 
wise rotation), should be as shown in Fig. 53 and 54 
when setting the commutator. 

When the armature of a right-hand machine is in 
position, the commutator is turned on the shaft until 



segment No. 1 is in the same relative position as the 
last half of No. 1 coil; segment No. 2 should corres¬ 
pond with the last half of No. 2 coil, and segment No. 
3 with the last half of No. 3 coil, as shown on Figs. 51 
and 52. 

For left-hand machines, see Figs. 53 and 54. 

The distance from the tip of the brush, which is on 
top, to the left-hand edge of No. 2 segment on a right- 
hand machine, or to the right-hand edge of No. 3 seg- 










94 


ELECTRICITY FOR ENGINEERS 


ment in a left-hand machine is called the lead, and 
should be made to correspond with the following 
table. 




TABLE OF 

LEADS 




DRUM ARMATURES. 

RING ARMATURES. 

C 12 

a inch positive 

R12 

ft 

inch positive 

C 2 

3 “ 

i 4 

K 2 

F 

4 4 

4 4 

E 12 

ft “ 

i i 

M 12 

1 

¥ 

4 4 

negative 

E 2 

i “ 

i 4 

M 2 

1 

2 

4 < 

4 4 

H 12 

i “ 

4 4 

LD 12 

1 

¥ 

4 4 

positive 

H 2 

1 44 

(t 

LD 2 

1 

IT 

4 4 

4 4 




MD 12 


4 4 

4 4 




MD 2 

13 

32 

4 4 

44 


Place the screws in the binding posts at the lower 
ends of the sliding connections, and put on the dash 
pot connections between the brushes, with the heads 
of the connecting screws outward. In every case the 
barrel part of the dash pot is connected to the top 
brush-holder, and plunger part to the bottom brush- 
holder. 

See that the field and regulator wires are connected 
and that all connections are securely made. 

When all connections have been made, make a care¬ 
ful examination of screws, joints and all moving parts. 
They must be free from stickiness and not bind in any 
position. 

To determine when the machine is under full load, 
notice the position of the regulator armature, which 
should be within }i in. of the stop. At full load the 
normal length of the spark on the commutator should 
be about in. If it is less than this, shut down the 
machine and move the commutator forward or in the 
direction of rotation until the spark is of the desired 
length. If the spark is too long, move the commu¬ 
tator back the proper amount. 

A general view of the complete dynamo is given in 




ELECTRICITY FOR ENGINEERS 


95 


Fig. 55, and will help explain the regulator used with 
this system. 

The regulator is fastened to the frame of the machine 
by two short bolts. On the right-hand machine its 
position is on the left-hand side, as shown in Fig. 55. 
On the left-hand machine, i.e ., one which runs clock¬ 
wise, its position is on the opposite side. Before fill- 



figure 55 . 


ing the dash pot D with glycer.ne, see that the 
regulator lever and its connections, brush yokes, etc., 
are free in every joint, and that the lever L can move 
freely up and down. Then fill the dash pot D with 
concentrated glycerine. The long wire from the 
regulator magnet M is connected with the left-hand 
binding post P of the machine, and the short wire with 














96 


ELECTRICITY FOR ENGINEERS 


the post P 2 on the side of the machine. The inside 
wire of the field magnet, or that leaving the iron flange, 
of the left-hand field should be connected into post P 2 
also, as shown in Fig. 55. The electric circuit (see 
Fig. 56) should be complete from post P 1 , on the con¬ 
troller magnet, through the lamps to the post N on the 
machine, through the right-hand field magnet C, to 
the brushes B 1 B 1 , through the commutator and arma¬ 
ture to the brushes B B, through the left-hand field C, 



to posts P 2 and P, thence to posts P 2 and P on the con¬ 
troller magnet, through the controller magnet to P 1 . 
The current passes in the direction indicated by the 
arrows 

When an arc machine is to be run frequently at a 
small fraction of its normal capacity, the use of a light 
load device is advisable to secure the best results in 
regulation. 

The rheostat for this purpose (see Fig. 57) is con¬ 
nected in shunt with the right field of the generator. 













































ELECTRICITY FOR ENGINEERS 


97 


Facing the rheostat with the right binding posts at the 
bottom, the contact on the right side or No. I gives 
open circuit and throws the rheostat out of use. Point 
No. 2 gives a resistance of 44 to 46 ohms and Point 
No. 3 gives a resistance of 20 to 22 ohms. 

This rheostat with a 75-light machine allows the fol¬ 
lowing variations: Point 1, 75 to 48 lights; Point 2, 
48 to 25 lights; Point 3, 25 lights or less. For use with 



FIGURE 57 . 


other sizes of generators, the adjustment of the rheo¬ 
stat must be made to suit the conditions. 

When the rheostat is in use, the sparks at the com¬ 
mutator will be somewhat larger than normal, but will 
not be detrimental. 

The controller magnet (see Fig. 58) is to be fastened 
securely by screws to the wall or some rigid upright 
support, taking care to have it perfectly plumb. It is 
connected to the machine in the manner shown in Fig. 
55, i.e., the binding post P 3 on the controller magnet is 









98 


ELECTRICITY EOR ENGINEERS 


connected to the binding post P 3 (see Fig. 55) on the 
end of the machine, and likewise the post P on the 
controller to the post P on the leg of the machine; 
the post P 1 forms the positive terminal from which the 
circuit is run to the lamps and back to N. 

Great care should be taken to see that the wires P P 



and P 3 P 3 are fastened securely in place; for if connec¬ 
tion between P and P should be impaired or broken, 
the regulator magnet M would be thrown out of action, 
thus throwing on the full power of the machine, and if 
the wire P 2 P 2 should become loosened, the full power 
of the magnet M would be thrown on, and the regu- 










































































































































































ELECTRICITY FOR ENGINEERS 99 

lator lever L, rising in consequence, would greatly 
weaken or put out the lights. 

The wires leading from the controller magnet to the 
machine should have an extra heavy insulation. 

Care should be taken in putting up the controller 
magnet that the following directions are followed: 

1. The cores B of the axial magnets C C must hang 
exactly in the center, and be free to move up and 
down. 

2. The screws fastening the yoke or tie pieces to the 
two cores must not be loosened. 

3. The contacts O must be firmly closed when the 
cores are not attracted by the coils C C, which is the 
case, of course, when no current is being generated by 
the machine, and when the cores are lifted, the con¬ 
tacts must open from fa in. to in.; a greater open¬ 
ing than 3^ in. has the effect of lengthening the time 
of action of the regulator magnet. This tends to ren¬ 
der the current unsteady, and in case of a very weak 
dash pot or short circuit might cause flashing. Adjust¬ 
ment must be made if necessary by bending the lower 
contact up or down, taking care that it is kept parallel 
with the upper contact, so that when they are closed, 
contact will be made across its whole width. If this 
adjustment is not properly made there will be destruc¬ 
tive sparking on a small portion of the contact surfaces. 

4. All connections must be perfectly secure. 

5. The check nuts N must be tight. 

6. The carbons in the tubes L must be whole. These 
carbons form a permanent shunt of high resistance 
around the regulator magnet M, and if broken will 
cause destructive sparking at contacts O, burning them 
and seriously interfering with close regulation of the 
generator. In case a carbon should become broken, 

L. of C. 


100 electricity for engineers 

temporary repairs may be made by splicing the broken 
pieces with a fine copper wire. 

To keep the action of the controller perfect the con¬ 
tacts O should be occasionally cleaned by inserting a 
folded piece of fine emery cloth and drawing it back 
and forth. 

The amount of current generated by each machine 



figure 59 . 


depends upon the adjustment of the spring S. If the 
tension of this spring is increased the current will be 
diminished; if the tension is diminished, the current 
will be increased. 

In starting these dynamos when the armature has 
reached its proper speed, the short circuiting switch on 
the frame should be opened. This method allows the 






































































































ELECTRICITY FOR ENGINEERS 


101 


generator to take up its load gradually, and is a very 
important point in the handling of the machine. 

Arc Switchboards. Fig. 59 shows a general view of 
the Thomson-Houston plug switchboard. A rear view 
of the same board is given in Fig. 60. 

In a standard panel the number of horizontal rows 
of holes equals one more than the number of gener¬ 
ators. The vertical holes are always twice the number 
of generators. The positive leads of the generators are 



figure 60 . 

attached to the binding posts on the left-hand ends of 
the horizontal conductors. The negative leads are 
connected to the corresponding binding posts at the 
right-hand end of the board. 

The positive line wires are connected to the vertical 
straps on the left, and the negative wires to the similar 
straps on the right of the center panel. 

If a switchboard plug be inserted in any of the holes 
of the board, it puts the corresponding generator lead 







102 


electricity for engineers 


and the line wire in electrical connection, but as the 
positive line wires are back of the positive generator 
leads only, it is not possible to reverse the connection 
of the line and the generator accidentally, though any 
other combinations of lines and generators can be 
made readily and quickly. 

The holes of the lower horizontal rows have bushings 
connected with the vertical straps only. Plugs con¬ 
nected in pairs by flexible cable and inserted in the 
holes put the corresponding vertical straps in connec¬ 
tion as needed, and normally independent lines maybe 
connected when one generator is required to supply 
several circuits. 

Lines and generator leads may be transferred, while 
running, by the use of these cables, without shutting 
down machines or extinguishing lamps. 

The standard boards are arranged for an equal num¬ 
ber of generators and circuits, but special boards for 
any ratio of circuits to generators can be built. 

As it is sometimes convenient, even in small plants, 
to interchange lines and generators without shutting 
down machines, a special transfer cable with plugs has 
been devised. This serves the same purpose as the 
regular transfer cable, but the plugs may be used in 
any of the holes of the switchboard, as they are insu¬ 
lated, except at the tip, and when inserted connect 
with the line strips only. 

The transfer of circuits from one generator to 
another gives trouble to dynamo tenders who are not 
familiar with the operation of these plug switchboards. 
Fig. 61 illustrates the successive steps for transferring 
the lamps of two independent circuits from two genera¬ 
tors to one without extinguishing the lamps on either 
circuit. 


ELECTRICITY FOR ENGINEERS 


103 



i 


2 

3 


e> 


n 


o 

0 

o 

o 

r t 

-e 

-e 

o 

o 

o o 

o 

o 

o 

o o 

o 


-e—e 


o 


2 

3 


l 


2 

3 


rz 


c 


o o 
o o 
o o o o 

o o o o 


zt 


-e—& 


-©—e 
o o o o 
o o o o 


i 


2 

3 



FIGURE 61. 

























































































104 


ELECTRICITY FOR ENGINEERS 


This process is a very simple example of switch¬ 
board manipulation, but illustrates the method used 
for all combinations. 

The location of plugs is shown by the black circles, 
which indicate that the corresponding bars of the 
horizontal and vertical rows are connected. 

Circuit No. I and No. 2, running independently from 
generators No. I and No. 2 respectively, are to be 
transferred to run in series on generator No. 2. 

In A, Fig. 6i, are two circuits running independently; 
in B the positive sides of both generators and circuits 
are connected by the insertion of additional plugs. 

At C both generators and circuits are in series. 

Next insert plugs and cables as shown in D. Then 
withdraw plugs on row corresponding to generator No. 
I, and the circuits No. I and No. 2 are in series on 
machine No. 2, and machine No. I is disconnected as 
at E. 

Similar transfers can be made between any two cir¬ 
cuits or machines, and by a continuation of the process 
additional circuits can be thrown in the same machine. 
The transfer of the two circuits to independent genera¬ 
tors is accomplished by reversing the process illus¬ 
trated. 

Fig. 62 shows the wiring and connections of the 
Western Electric Co.’s series arc switchboard. At the 
top of the board are mounted six ammeters, one being 
connected in the circuit of each machine. On the 
lower part of the board are a number of holes, under 
which, on the back of the board, are mounted spring 
jacks to which the circuit and machine terminals are 
connected. For making connections between dynamos 
and circuits, flexible cables terminating at each end in 
a plug, are used; these are commonly called “jump- 


ELECTRICITY FOR ENGINEERS 


105 


ers.” The board shown has a capacity of six machines 
and nine circuits, and with the connections as shown 
machine I is furnishing current to circuit I, machine 2 
is furnishing current to circuits 2 and 3, and machine 4 
is furnishing current to circuits 4, 5 and 7. In con¬ 
necting together arc dynamos and circuits the positive 
of the machine (or that terminal from which the cur¬ 
rent is flowing) is connected to the positive of the cir¬ 



cuit (the terminal into which the current is flowing). 
Likewise the negative of the machine is connected to 
the negative of the circuit. Where more than one cir¬ 
cuit is to be operated from one dynamo, the - of the 
first circuit is connected to the 4 - of the second. At 
each side of the name plate (at 3, for instance) there 
are three holes. The large hole is used for the per¬ 
manent connection, while the smaller holes are used 
for transferring circuits, without shutting down the 




























































































106 


ELECTRICITY FOR ENGINEERS 


dynamo. Smaller cables and plugs are used for 
transferring. If it is desired to cut off circuit 5 from 
machine 4, a plug is inserted in one of the small holes 
at the right of 4, the other plug being inserted in one 
of the holes at the left of 7. Circuit 5 would now be 
short circuited, and the plug in the + of 5 can now be 
transferred to the permanent connection in the + of 7, 
and the cords running to 5 removed. If it is desired 
to cut in a circuit, say circuit 6 onto machine 2, insert a 
cord between the — of circuit 2 and the + of 6 and an¬ 
other between the — of 6 and the + of 3. Now pull the 
plug on the cord connecting — of 2 and the + of 3 and 
insert the permanent connections. In cutting in cir¬ 
cuits, if they contain a great number of lights, a long 
arc may be drawn when the plug between 2 and 3 is 
pulled, and it is sometimes advisable to shut down the 
machine when making a change of this kind. 




CHAPTER V 


MOTORS. — ALTERNATING CURRENT MOTORS. 

Motors. Any dynamo may be used as a motor and con¬ 
sequently we have as many types of motors as there are 
types of dynamos. The pull of a motor depends upon 
the repulsion and attraction between the lines of force, 
or magnetism of the wire and core of the armature and 
that of the fields. We have seen that in a dynamo, as 
we force a wire through a magnetic field, current is 
generated. The more current there is generated or 
flowing in such a wire, the greater will be the expendi¬ 
ture of power necessary to force such a wire through a 
magnetic field; in other words, the currents flowing in 
the wires of a dynamo armature, always tend to drive 
the armature in a direction opposite to that in which it 
is being driven. 

If, then, instead of revolving a dynamo armature by 
mechanical means, we connect it to a source of elec¬ 
tricity and allow a current to flow through it we must 
obtain motion, and the direction of this motion will 
depend upon the direction in which the current flows, 
so long as this current does not alter the magnetism of 
the fields. 

We have already seen that the electric motor is built 
exactly like a dynamo; consequently, as its armature 
revolves it not only does useful work, such as turning 
whatever machinery it is belted to, but it also gener¬ 
ates an electromotive force. For instance, if a motor, 
running at full speed and receiving current from a 

107 


108 


ELECTRICITY FOR ENGINEERS 


dynamo (Fig. 63), were suddenly disconnected by 
opening the main switch, it would at once begin acting 
as a generator and sending out current. This can be 
easily seen with any motor equipped with a starting 
box, such as shown; for the current from the motor 
will continue to energize the fields and the little mag¬ 
net M so as to hold the arm of the starting box until 
the motor has nearly come to rest. If it were not for 
the current generated by the motor, this arm would fly 
back the instant the switch is opened. 

The electromotive force set up by a motor always 
opposes that of the dynamo driving it; that is, the 
current which the motor tends to send out would flow 
in the opposite direction to that which is driving it. 

This may be compared, and is somewhat similar, to 
the back pressure of the water which a pump is forcing 
into a tank. If the check valves were removed and 
the steam pressure shut off, the water would tend to 
force the pump backward. 

This electromotive force is called the counter elec¬ 
tromotive force of the motor. The counter electro¬ 
motive force of the motor varies with the speed of the 
motor and also limits the speed of the motor, for it is 
obviously impossible that a motor should develop 
higher counter E. M. F. than the E. M. F. of the 
dynamo driving it. 

This highest possible speed of a motor is, then, that 
speed at which its counter E. M. F. becomes equal to 
the E. M. F. of the dynamo supplying the current, and 
this is the speed which would be obtained were the 
motor doing no work and running without friction. 
This condition is impossible in practice, and the 
counter E. M. F. of the motor is always less than the 
E. M. F. of the dynamo. In order to speed up a 


ELECTRICITY FOR ENGINEERS 


109 


motor we must arrange it so that it must run faster in 
order to develop an E. M. F. equal to that of the 
dynamo; we can do this by lessening the number of 
turns of wire on the armature, or by lessening the 
magnetism of the fields. In doing so, however, we 
also lessen the capacity of the motor for performing 
work. 

The power that can be obtained from an electric 
motor depends upon two things: the current flowing in 
its armature coils and the strength of magnetism devel¬ 
oped in the fields. 

Assuming the fields as remaining constant, the power 
of the motor must then vary as the current flowing 
through it. Suppose we have a motor being driven by 
an E. M. F. of no volts and it is doing no work; it 
will be running at full speed and its counter E. M. F. 
will therefore also be very near no volts. If now a 
load be thrown on this motor, it must get more current 
in order to develop the necessary power to carry the 
load. 

Throwing on the load will decrease the speed of this 
motor, and consequently its counter E. M. F. will fall, 
say to ioo volts. The E. M. F. of the dynamo being 
no and the counter E. M. F of the motor ioo, there 
will be considerable current forced through the arma¬ 
ture of the motor, so that it can now handle the load. 

The current in the armature at all times will equal 
E - E' 

—=— where E is the electromotive force of the 

K 

dynamo, E' the counter electromotive force of motor, 
and R the resistance of the motor armature. In order 
that a motor should keep a nearly uniform speed, for 
varying loads, the resistance of its armature should be 
very low, for then a slight drop in counter E. M. F. 



no 


ELECTRICITY FOR ENGINEERS 


will allow considerable current to flow through the 
armature'. The above applies particularly to the shunt 
motor shown in Fig. 63. In this diagram C is a double 
pole fuse block, S the main controlling switch, R the 
starting box, or rheostat, M the magnet, which holds 
the arm of the starting box in place when it is brought 



over against it, F the fields, and A the armature of the 
motor. 

The current enters, say at the right hand fuse, and 
passes to the starting box and along the fine wires 
shown in dotted lines through the fields of the motor 
and coil M to the other fuse. The fields of the motor 
and the little magnet M are now charged, but as yet 



















































ELECTRICITY FOR ENGINEERS 


111 


there is no current passing through the armature and 
no motion. We now slowly move the arm on the start¬ 
ing box to the right; this admits a little current, 
limited by the resistance in the starting box, to the 
motor armature and it begins to revolve, and as we 
continue to move the arm to the right, the armature 
gains in speed because we admit more current to it by 
cutting out more and more resistance. When the 
armature attains full speed, the arm comes in contact 
with the little magnet M, and is held there by magnet¬ 
ism. The whole object of the starting box is to check 
the inrush of current, while the armature is developing 
its counter E. M. F. or back pressure. 

When the armature has attained its normal speed, 
the starting box is no longer in use. If for any reason 
the current ceases to flow, the little magnet M loses its 
magnetism and releases the arm, which (actuated by a 
spring) flies back and opens the circuit so that, should 
the current suddenly come on again, the sudden inrush 
will not damage the armature. 

In Fig. 64 are shown the connections of a series 
wound motor with an automatic release spool on the 
starting box of a sufficiently high resistance so it can be 
connected directly across the circuit. This becomes 
necessary since the field windings are in series with the 
armature. 

The speed of a series motor may be decreased by 
connecting a resistance in series with the motor and 
may be increased in speed by cutting out some of the 
field windings. In electric railway work where two 
motors are used on one car, they are usually connected 
in series with each other in starting up and then in 
parallel with each other while running at full or nearly 
full speed. The series motor is well adapted to such 


112 ELECTRICITY FOR ENGINEERS 

work as electric railway work, or for cranes and so 
forth, because it will automatically regulate its speed 
to the load to be moved, exerting a powerful torque 
at a low speed while pulling a heavy load. Such a 
motor, however, requires constant attendance when the 



load becomes light, as it will tend to “run away” 
unless its speed is checked. 

In Fig. 65 we have a diagram of a compound wound 
motor connected with a type of starting box that cuts 
out the armature when current has been cut off the 
lines supplying the motor, as before explained. In 
addition to this there is another electro magnet which 
is traversed by the main current on its path to the 
armature. Should the motor be overloaded by some 





























































ELECTRICITY FOR ENGINEERS 


113 


means, the current flowing to the armature would 
exceed the normal flow. The magnetism thus pro¬ 
duced would overcome the tension of a spring on the 
armature of the so-called “overload magnet” and cause 
it to short circuit the magnet which holds the resist¬ 
ance lever and allow it to fly back and open the arma¬ 



ture circuit. By so doing the liability of burning out 
the armature due to overload is reduced to a minimum. 

The compound motor may be made to run at a very 
constant speed, if the current in the series winding of 
the fields is arranged to act in opposition to that of the 
shunt winding. In such a case an increase in the load 
of a motor will weaken the fields and allow more cur¬ 
rent to flow through the armature without decreasing 

































































114 


electricity for Engineers 


the speed of the armature, as would be necessary 
in a shunt motor. Such motors, however, are not 
very often used, since an overload would weaken the 
fields too much and cause trouble. 

If the current in the series field acts in the same 



direction as that of the shunt fields, the motor will 
slow up some when a heavy load comes on, but will 
take care of the load without much trouble. Fig. 66 
shows a starting box arranged as a speed controller. 
It differs from other starting boxes only in so far that 
the resistance wire is much larger and that the little 





















































ELECTRICITY FOR ENGINEERS 


115 


magnet will hold the arm at any place we desire, so 
that if we leave the arm at any intermediate point the 
motor will run at reduced speed. This sort of speed 
regulation can be used only where the load on the 
motor is quite constant. If the load varies, the speed 
will vary. Another and a better way of varying the 
speed of motors consists in cutting a variable resist¬ 
ance into the field circuit, as more resistance is cut 
into the circuit the fields become weaker and the 
motor speeds up. If possible, motors should be so 
designed that they can operate at their normal speed, 
and they will then cause little trouble. 

Motors have much the same faults as dvnamos, but 
they make themselves manifest in a different way. 
An open field circuit will prevent the motor from start¬ 
ing and will cause the melting of fuses or burning out 
of an armature. The direction of rotation can be 
altered by reversing the current through either the 
armature or the fields. If the current is reversed 
through both, the motor will continue to run in the 
same direction. A short circuit in the fields, if it cuts 
out only a part of the wiring, will cause the motor to 
run faster and very likely spark badly. If the brushes 
are not set exactly opposite each other, there will also 
be bad sparking. If they are not at the neutral point, 
the motor will spark badly; brushes should always be 
set at the point of least sparking. If it becomes neces¬ 
sary to open the field circuit, it should be done slowly, 
letting the arc gradually die out; a quick break of a 
circuit in connection with any dynamo or motor is not 
advisable, as it is very likely to break down the insula¬ 
tion of the machine. 

The ordinary starting box for motors is wound with 
comparatively fine wire and will get very hot if left in 


116 


ELECTRICITY FOR ENGINEERS 


circuit long. The movement of the arm from the first 
to the last point should not occupy more than thirty 
seconds, and if the armature does not begin to move at 
the first point the arm should be thrown back and the 
trouble located. 

Alternating Current Motors. By a proper combination 
of two phase or three phase currents it is possible to 
produce a revolving magnetic pole. By placing inside 
of the apparatus which produces this revolving mag¬ 
netic pole a suitable short circuited armature, this 
armature will be dragged around by the revolving pole 
in much the same way that a short circuited armature 
in a direct current machine would be dragged around 
if the fields were revolved. Such a machine is called 
an induction motor. The armature will revolve with¬ 
out any current entering it from the external circuit. 
This does away with commutators, collector rings, 
brushes, brush-holders, and in fact many of the parts 
which are so necessary in direct current machines. 
The rapidity of the alternations in the external circuit 
determines the speed of the motor. 

Some alternating current motors are known as 
"synchronous” motors. What is meant by synchro¬ 
nous is, occuring at the same time, or in unison. As 
an example, suppose two clocks are ticking just alike 
so that the pendulums start and stop at the same time; 
we would hear but one tick. These two clocks would 
then be in synchronism. If an alternating current 
generator has 32 field coils and revolves at the rate of 
60 R. P. M., then a synchronous motor with only 4 
field coils would revolve at the rate of 480 R. P. M. 
This motor would operate in synchrony with the gener¬ 
ator and yet would make 480 R. P. M. while the 
generator made 60 R. P. M. 


f 


CHAPTER VI 


Fuses and Circuit Breakers. Fuses are metal wires or 
strips, generally made of an alloy of lead and antimony, 
the amount of each metal used being so proportioned 
that the wire will melt at a certain temperature. This 
metal is very similar to that used in the fusible plugs 
in boilers. These fuse strips or fuse wires are placed 
in the various circuits in such a manner that the current 
must first flow through the fuse before entering the lights, 
motors or other electrical apparatus. If a short circuit 
should occur, there would be an excessive amount 
of current flow through the fuse and the temperature 
of the metal would be raised to the point where it would 
melt and open the circuit. This would cut off the current 
and save the electrical apparatus from being damaged 
by the excessive current. Fuses are placed in the var¬ 
ious circuits in accordance with the rules and regulations 
of the National Board of Fire Underwriters. These rules 
require a fuse to be placed in the circuit of every piece 
of electrical apparatus liable to be short circuited, and 
also at points where small wires are tapped onto larger 
ones, unless the main fuse in the larger wire is small 
enough to protect the smallest wire in the circuit. The 
ordinary commercial fuse wire is not intended to melt 
until the current has reached a strength of about twice 
the number of amperes marked on "the fuse. A few 
good points to remember in regard to fuses are as fol¬ 
lows: Unless the fuses are of the new enclosed type 
(fuses entirely encased in small tubes) or unless they 
are under the eye of a constant attendant, they should 
be enclosed in fireproof boxes. This should be done 
to minimize the chance of the red hot metal from a 

117 


118 


ELECTRICITY FOR ENGINEERS 


melted fuse dropping into some inflammable material. 
It is a very good plan to enclose all fuses. Fuses 
placed in a hot room will blow at a lower increase in 
current than those in a cool room. Always use copper 
tipped fuses, both for the purpose of getting a good 
contact at the binding screw and for the reason that 
the blowing point of a fuse wire depends on the length 
of the wire. Two pieces of fuse wire of the same 
diameter, but of different lengths, will not blow with the 
same current because the cooling effect of the terminals 
is greater with the shorter fuse. 

In the larger size fuse strips see that the contacts 
between the fuse terminal and the binding post are free 
from dirt and that there is plenty of contact between 
them, otherwise the poor contact will heat up the ter¬ 
minal and the fuse strip and cause it to blow at a much 
lower current strength than that for which it is marked. 
Oil between the contacts will cause heating and the 
same result. 

From the fact that when a fuse strip has blown the 
current will be off the circuits which are protected by 
the strip until the fuse has been replaced, and this 
takes some time, another device known as the circuit 
breaker has come into general use. The circuit breaker 
is simply a knife switch equipped with a spring which 
tends to open it, and is held in place by a small catch. 
The current passing through the switch also passes 
through the winding of a small solenoid on the inside 
of which is an iron core. When the current passing 
through the solenoid exceeds a certain amount, the 
iron core is drawn up into the solenoid, and in doing 
so strikes the catch holding the switch and releases it, 
thus opening the switch and cutting off the current. 
Circuit breakers are nearly always installed in the cir- 


ELECTRICITY FOR ENGINEERS 


119 



67. 


FIGURE 














120 


ELECTRICITY FOR ENGINEERS 


cuits of generators, although fuses are also used. The 
fuse is rated higher than the circuit breaker, so that 
the circuit breaker will operate first and the fuse only 
operates when the circuit breaker fails to work. Cir¬ 
cuit breakers are also used to a large extent in protect¬ 
ing large motors, and the small overload devices used 
on motor starting boxes are simply circuit breakers. 
Fig. 67 shows a view of an I-T-E circuit breaker. S is 
the solenoid and I the moveable iron core. This core 
is adjustable, by means of the washer W, so that it will 
operate at whatever current desired. L is the catch 
which holds the switch. Carbon contact pieces, C C, 
are so arranged that the current is broken on them, 
thus taking the arc off the blades. In Fig. 68 a dia¬ 
gram of a circuit breaker used for the protection of a 
motor is shown. In this case the circuit breaker is 
double pole; while the one shown in the preceding fig¬ 
ure is single pole. 

For small work, such as tap lines and small motors, 
the circuit breaker is too expensive to warrant its use, 
but for capacities of 50 amperes and over it is advisible 
to use the circuit breaker. Circuit breakers are also 
designed and used to prevent the liability of short cir¬ 
cuits between generators connected in parallel, due to 
the reversal of polarity of one of the dynamos. In other 
words, should one of the dynamos become reversed in 
polarity while working in parallel with other machines, 
the polarity circuit breaker would open the machine- 
switch and cut it out. Circuit breakers of this descrip¬ 
tion are also used in charging storage batteries. Some¬ 
times circuit breakers are referred to as overload 
switches. The mechanical operation of these instru¬ 
ments can be readily understood when examined, as 
they are all of a very simple mechanical construction. 


ELECTRICITY FOR ENGINEERS 


121 


LINE 

J u 


CIRCUIT 

BREAKER 


D.P.S.T. 

SWITCH 



FIGURE 68, 




























































CHAPTER VII 


ALTERNATING CURRENT DYNAMOS 

Alternating current dynamos are operated upon the 
same general principle of magnetic induction as that 
involved in continuous current dynamos. The 
mechanical construction, however, differs considerably 
in the two types of machines. The current produced 
in the two types is identical, but in the direct current 
machine this current is rectified by means of a com¬ 
mutator; that is, the current constantly flows out one 
wire and back in the other wire, never changing in 
direction in the external circuit. In the alternating 
current dynamo the current is sent to the line exactly 
as it is generated in the armature, flowing out one wire 
and back on the other and then reversing and flowing 
out on the wire on which it has just flowed in, and back 
on the wire on which it had formerly flowed out. An 
illustration which will more fully explain this action 
can be found by supposing the two ends of the cylinder 
of a piston pump were connected by means of a pipe 
and then, having done away with all the valve move¬ 
ments, the pumps were started. At the beginning of 
the stroke, water would be forced out one side of the 
cylinder around the pipe into the other side of the 
cylinder, and after the piston had reached the end of 
the stroke and started back, the water would then take 
a return course back to where it had started. In this 
case the pump could be likened to the dynamo and 
the pipe to the wires, and the current to the water 
flowing back and forth. The form and winding of 

122 


ELECTRICITY FOR ENGINEERS 


123 


alternating current dynamos varies considerably, but 
they generally follow the plan shown in Fig. 69. In 
the figure the pole pieces are alternately north (N) and 
south (S), while the armature is wound with the same 
number of poles, with the winding so arranged that 
the poles alternate. The fields are excited by direct 
current passing over the field coil windings. This 



direct current is usually obtained from another source 
aside from the current generated in the armature of 
the alternating current dynamo. A separate dynamo, 
called an exciter, is employed for supplying the cur¬ 
rent to the fields. There are some types of so called 
“composite wound alternating current dynamos” in 
which a part of the current from the alternator arma- 























124 


ELECTRICITY FOR ENGINEERS 


ture is rectified or commutated by means of a commu¬ 
tator mounted on the same shaft with the armature, 



figure 70 . 


and this commutated current passed around the field 
coils in a manner similar to the direct current com- 

























































































































ELECTRICITY FOR ENGINEERS 


125 


pound wound dynamo. In Fig. 70 we have a diagram 
of connections of a composite wound machine made by 
the General Electric Company. It will be noticed that 
in connection with this dynamo we still employ a sepa¬ 
rate direct current exciting machine. The object of this 
composite winding is the same as with the compound 
wound direct current dynamo, namely, regulation 
under variable loads without the necessity of changing 
the strength of the field exciting current from the 
exciter dynamo. The winding of the alternate current 
armature consists of the same number of armature coils 
as there are pole pieces in the fields of the machine. 
The outer end of the first armature coil is left free to 
be connected to one of the collector rings, while the 
other end of the coil is connected to the inner end of 
the second coil; the outer end of the second coil is 
connected to the outer end of the third coil, and so on 
through the entire armature. In this class of winding 
you can readily see that while the coils connected from 
the underside or inner ends are under the influence of 
one polarity of field magnetism, the armature coils 
connected from the outer side are under an opposite 
magnetic influence. The purpose of forming the arma¬ 
ture circuit in this manner may be fully understood 
when it is remembered that the magnetism from the 
north pole of a magnet will induce a flow of electricity 
in a coil of wire in a given direction, while the mag¬ 
netism of the south pole will induce a flow of current 
in an opposite direction. Now, for the reasons just 
explained, the current in all of the coils of the arma¬ 
ture will flow in the one direction, but as the armature 
is rotated sufficiently to move the coils from the influ¬ 
ence of one pole to the influence of the opposite pole 
which is next to it, the action of all the magnetic poles 


126 


ELECTRICITY FOR ENGINEERS 


of the field reverse all the inductions in the armature 
coils and cause the current to flow in an opposite 
direction. The number of reversals occurring during 
a revolution is determined by the number of poles that 
the armature coils pass during one revolution. One of 
these armature coils we will assume to be under a 
north magnetic influence and in its rotation it passes 
through a south magnetic influence, thence into a 
north magnetic influence again. The current has now 
alternated or reversed its direction of flow twice and 
has passed through what is called one cycle. If the 
current .were making 120 alternations or passing 
through 60 cycles in one second, it would be known as 
making 60 cycles or alternating at the rate 7,200 alter¬ 
nations per minute. These are the general terms used 
in designating alternating currents. 

By tracing out the circuits in Fig. 70, it will be seen 
that, assuming the current to be flowing into the col¬ 
lector ring R, it will pass through the upper half of the 
armature winding and out to the commutator C, where 
a part of it will be commutated (or changed into direct 
current), then flowing back around the lower half of 
the armature windings and out to the other collector 
ring R'. On the commutator C the upper line coming 
from the armature is connected to each alternate seg¬ 
ment, while the lower line is connected to the remain¬ 
ing segments. The amount of current which is thus 
rectified and flows around the two halves of the field 
winding, which are connected in parallel, is regulated 
by means of the German silver shunt. The fields are 
also energized by the current generated in the small 
dynamo known as the exciter. 

In Fig. 71 is shown an alternating current dynamo 
with its separate exciter The two collector rings are 


ELECTRICITY FOR ENGINEERS 127 

shown immediately at the right of the armature, while 
at the right of the collector rings is shown the commu¬ 
tator from which the current for the composite winding 
of the fields is taken. The current generated by the 
alternator is regulated in the same way as with direct 
current dynamos; that is, by varying the current sent 
around the field windings. This is accomplished by 
the use of a resistance box in series with the exciting 



FIGURE 71 . 


current or by means of a resistance box connected in 
the fields of the exciting dynamo. This latter regula¬ 
tion is of course the more economical, as there would 
be considerable energy wasted were a resistance used 
in the main exciting circuit. Alternating currents are 
generally used where currents are to be transmitted 
long distances, as for instance, where power is derived 
from a water fall situated some distance from the 



m 


ELECTRICITY FOR ENGINEERS 



point of use. Its adaptability for such work is 
apparent, because it can be generated at high voltages 
and transformed down to any voltage desired. It 
requires less copper to transmit it, due to the higher 
voltages employed. By the aid of transformers it can 
either be stepped up to a higher pressure or stepped 
down to as low a pressure or voltage as desired. 
Another great advantage is that, after it has been 
transmitted a considerable number of miles, by the aid 


figure 72 . 

of a rotary converter it can be converted into direct 
current. 

Rotary transformers which transform the alternating 
current to a direct current are simply alternating cur¬ 
rent motors connected to direct current dynamos. 
Sometimes these machines are mounted on the same 
shaft; sometimes they are belted together, and in some 
cases the same windings are used for both machines; a 
commutator being mounted at one side of the armature 






ELECTRICITY FOR ENGINEERS 


m 


from which direct current is taken while the alter¬ 
nating current is taken into the armature on a pair of 
collector rings on the opposite end of the shaft. In 
big. 72 is shown a view of a rotary transformer where 
the alternating current is taken in at the right, and 
direct current taken off at the commutator on the left. 

By single phase we understand that the current flows 
out, gradually increasing in strength, then dying away 
and reversing in direction and again increasing and 
dying away. This action is shown by the curve in 



figure 73 . 


Fig. 73. Although the single phase alternating cur¬ 
rent system is in advance of the direct current system 
for electrical power transmission, because permitting 
electrical power to be transmitted long distances at 
high potential, which can be readily increased or 
reduced by means of transformers, the single phase 
system is limited by the difficulty in obtaining a satis¬ 
factory self starting motor; therefore the use of the 
single phase current has been confined almost entirely 
to transmitting current for lighting. The development 
of the polyphase (two phase and three phase) alter- 



130 


ELECTRICITY FOR ENGINEERS 


nating systems possess all the advantages of the single 
phase system and at the same time permits the use of 
motors having not only most of the valuable features 
of the continuous current motors, but also some advan¬ 




tages over them. In the two phase system two cur¬ 
rents displaced 90 degrees from each other and 
otherwise exactly similar to the single phase currents 
are used. In the three phase system three currents 
separated 120 degrees are used. These currents are 
shown in Fig. 74. 



FIGURE 75 . 


• v 

In Fig. 75 is shown the principle upon which the 
transformer used in alternating current work are opera¬ 
ted. Two separate coils of wire are wound on a ring 










ELECTRICITY FOR ENGINEERS 131 

of laminated iron. One of the coils contains a num¬ 
ber of turns of fine wire, while the other contains only 
a few turns of large wire. When an alternating cur¬ 
rent is sent around the coils of fine wire, generally 
called the primary, a current will be induced in the 
coil of heavy wire, or secondary. The amount of cur¬ 
rent induced in the larger wire will be relatively 
greater in amperes and less in potential than that of 
the fine wire circuit. This ratio is almost entirely 
dependent upon the relative number of turns existing 



between the large and the small wires. To illustrate, 
suppose we had a current of io amperes at a pressure 
of 1,000 volts in the primary, and there were ten times 
as many turns of wire in the primary coil as in the 
secondary, then we would get a current of ioo amperes 
at a pressure of ioo volts in the secondary coil. This 
same relation would hold true whatever the ratio 
between the number of turns on the two coils might 
be. In Fig. 76 is shown a core of iron having on one 
end a primary coil connected to a battery. On the 
other end of the core is another coil connected to the 






















132 ELECTRICITY FOR ENGINEERS 

ends of which is an incandescent lamp. By making 
and breaking the battery circuit the lamp may be made 
to flash up, due to the great voltage induced in the 
secondary coil. This is a good thing to remember 
when working with a dynamo or motor. Do not 
quickly break the shunt field connection, as the 
increased voltage due to the current induced by the 
field magnet when the circuit is broken is liable to 
puncture the insulation and necessitate the re-winding 
of the field coil. 


CHAPTER VIII 


METERS 

Volt and Ampere Meters. Two of the most important 
instruments used in electrical work are the voltmeter 
and amperemeter, the latter generally called ammeter. 
Classed with these instruments is a meter of an im¬ 
portant nature called the wattmeter. We will first 
become acquainted with the voltmeter, which is an 
instrument, as its name implies, for measuring the 
voltage or potential or electromotive force between two 
wires. The general construction of this instrument is 
shown in Fig. 77. 

In this diagram we show an instrument on the order 
of the Weston meter. This will serve as a good illus¬ 
tration that the operation of meters is very similar to 
the operation of motors. A permanent magnet, M, 
causes a magnetic flux across the air gap G, and 
situated in this gap is a bobbin, B, on which is wound a 
number of convolutions or turns of copper wire. The 
bobbin is made to revolve on jeweled bearings. The 
object of the jewel bearing is to have the instrument as 
much devoid of mechanical friction as possible. Two 
springs, S, one above and one below the bobbin, carry 
the current to the movable part of the meter. If the 
current is now caused to flow around the coil of wire, 
it will produce a torque or twist which will move the 
bobbin again the two hair springs, S. Like magnetic 
poles repel each other and unlike magnetic poles 
attract each other. The current flowing around the 

133 


134 


ELECTRICITY FOR ENGINEERS 


movable bobbin produces magnetism, and the quantity 
or strength of magnetism so produced is proportional 
to the amount of current which the pressure or voltage 



will force through the winding of the movable bobbin 
so that the bobbin will continue to move until the 
torque exerted by the current equals the counter torque 
exerted by the spiral springs. A pointer, fastened to 

















ELECTRICITY FOR ENGINEERS 


135 


the shaft upon which the bobbin is mounted, passes 
over a graduated scale and indicates the pressure or 
volts. The capacity of this meter in volts will vary as 
the resistance of the wire connected in series with the 
bobbin varies. We will assume that we have a meter 
whose pointer reads from o to 125 volts. If we desired 
this same meter to read from o to 250 volts, we would 
put a resistance in the meter which would be twice as 
great as the one contained in the meter when reading 
from o to 125 volts. The permanent magnet of this 
meter is made of Tungsten steel, and this steel is arti¬ 
ficially aged so that when the instrument leaves the 
factory the magnetizing power of the magnet will 
remain constant for a number of years. The current 
is brought into the instrument through the binding 
posts A and C, but before passing through the wire on 
the bobbin the current must pass over a path of very 
high resistance, R. This resistance is proportioned to 
the amount of pressure the meter is made to indicate, 
and in commercial construction instead of making 
bobbins of variable resistances, the bobbins are all 
made alike, and this dead resistance, R, is varied to 
comply with the pressure that it is to indicate with the 
instrument. In voltmeters used on,a 500 to 600 volt 
circuit, this resistance will measure from 65,000 to 
75,000 ohms. The current which flows through the 
winding on the bobbin at full voltage is very small, and 
when registering no volts amounts to about one seven- 
hundredth of an ampere. Since it is the number of 
ampere turns that produces the magnetic density in an 
electro magnet, it can be seen that even one seven- 
hundredth of an ampere, if passed around a bobbin a 
considerable number of times, will produce quite a 
strong magnetic flux and pull. Voltmeters are often 


136 


ELECTRICITY FOR ENGINEERS 


referred to as being “dead beat.” What is meant by 
dead beat is the tendency of the pointer to move from 
one position to another with very little or no swinging 
to and fro. In this type of voltmeter this dead beat 
effect is produced in the following manner: The core 
of the bobbin B being constructed of copper, when a 
current flows over the winding of the bobbin and causes 
it to revolve, eddy currents are produced in the copper 
(in much the same way that current is produced in the 
revolving armature of a dynamo), and these eddy cur¬ 
rents tend to arrest the motion of the bobbin. In the 
best voltmeter construction the resistance wire used is 
made of a metal which will not vary much in resistance 
at different temperatures. It can readily be seen that, 
were a meter which was constructed and correctly 
calibrated at 70 ° F., surrounding temperature, mounted 
on switchboard in an engine-room with the temperature 
at 90° or 95 0 , the meter would not register absolutely 
correct, because the resistance of the wire would be 
considerably increased, due to the increase of the sur¬ 
rounding temperature. The effect of this would be a 
smaller flow of current at an equal voltage through 
the bobbin in the meter, and consequently a smaller 
amount of magnetism and a lower reading of the in¬ 
strument. 

We will assume that a copper cable of about the size 
of one’s wrist is conducting a current of about 
three thousand amperes. Now, if a monkey wrench or 
hammer were to be lying within a few inches of this 
cable, before current was flowing, the monkey wrench 
or hammer would be attracted to the cable. The 
rapidity with which the monkey wrench would be 
attracted to the cable would be proportional to the 
weight of the iron in the wrench and the amount of the 


ELECTRICITY FOR ENGINEERS 


137 


current flowing through the cable. This, I think, will 
explain an electrical phenomenon which will assist us 
to understand what are called the magnetic vane volt¬ 
meters and ammeters. This principle is shown in 
Fig. 78. 

A certain amount of current passing over the path 
A, which consists of several turns of wire, will attract 
an iron form, B, mounted on the spindle with the 



figure 78 . 


pointer. The attraction will be proportional to the 
amount of current flowing over the copper conductor. 
The advantage of such an instrument is its simplicity, 
but the disadvantage is its inaccuracy. Its simplicity is 
apparent, and its inaccuracy is due to the residual 
magnetism that remains in the iron part B when the 
current through the conductor has been reduced. 
When the indicator is caused 1o move upward on the 
scale, the instrument will register practically correct, 







138 ELECTRICITY FOR ENGINEERS 

but as the flow of current over the conductor A dimin¬ 
ishes or decreases, the residual magnetism remaining 
in the iron part B will have a tendency to cause it to 
lag back. Amperemeters are constructed on practi¬ 
cally the same lines as explained in the construction of 
voltmeters, except that in ammeters the whole current 
to be measured passes through the coil A, this coil 
being made of comparatively few turns of large wire, 
while in voltmeters the resistance is very high. 
Ammeters are placed in series with one of the leads 
and voltmeters in shunt with the current to be meas¬ 
ured. In some ammeters a resistance block, usually 
called a shunt, is employed, over which the main cur¬ 
rent is caused to flow, and the ammeter is connected to 
both ends of this resistance block. In this way only a 
very small portion of the total current is caused to 
flow through the ammeter. In this case a milli-volt- 
meter, with the scale graduated to amperes, is 
employed. By Ohm’s law we know that the voltage is 
equal to the current times the resistance, E = CR. 
The resistance remaining constant, the voltage is pro¬ 
portional to the current, so that the amount of current 
sent through the milli-voltmeter or ammeter is exactly 
proportional to the current flowing through the shunt. 
Fig. 79 shows connections for ammeters which carry 
the entire current and those used with a shunt. 

The object of such a construction is apparent. In 
the installation of the switchboard, where each 
ammeter registers several thousand amperes, it is not 
necessary to construct the large conductors in such a 
manner that the total current is caused to flow through 
the ammeter. For each 1,000 amperes passing over 
the shunt only about one-half an ampere will pass 
through the ammeter, and the little bobbin will then 


ELECTRICITY FOR ENGINEERS 


139 


cause a deflection of the pointer in the meter and the 
pointer will register i } ooo amperes. Meters of this 
description are usually connected to their resistance 
blocks by a pair of No. 16 flexible lamp cords. When 
installing meters of this class, never cut off any of the 



figure 79 . 

\ 

flexible cord which is supplied with the ammeter, as 
the resistance of the cord becomes a part of the resist¬ 
ance in the meter. By cutting off some of this cord 
it can be readily seen that the meter will register more 
current than it should. 


i 























140 


ELECTRICITY FOR ENGINEERS 


Another kind of meter is constructed on the 
solenoid principle, and is shown in Fig. 80. In this 
instrument the helix is a bare copper wire and is wound 
in an open coil form. It is curved in the shape of a 
segment of a circle, the center of which is at the pivot 
on which the needle is suspended. The pointer or 
needle is attached and projects downward to the scale. 
The helix is made of copper rod or is cast to the shape 



figure 80 . 


required. Being of an open coil type, it is not neces¬ 
sary that it be insulated with insulating material 
because the air spaces between the turns becomes the 
insulation. Although not the best insulator by any 
means, there are few substances which possess better 
insulating qualities than air, although on account of its 
absorption of moisture, it becomes often a much poorer 
insulator than many other materials. In this type of 








ELECTRICITY FOR ENGINEERS 


141 


instrument it will be seen that as the number of 
amperes flowing over the coil is increased it produces 
an increased electromagnetic pull on the iron section 
or core entering it. As this electro magnetic pull is 



increased, the core moves up into the helix and causes 
a deflection of the pointer across the scale on the 
instrument. This type of instrument has the same 
objection as that of the magnetic vane instrument, 










































142 


ELECTRICITY FOR ENGINEERS 


namely, residual magnetism of the iron, and hence 
error in the reading while the current flowing is being 
diminished. 

Another style of simple ammeter or voltmeter is 
shown in Fig. 81. This instrument consists of a frame 
made of non-magnetic material, around which the wire 
is wound, the ends of the wires being connected to the 
binding posts. The armature of this instrument, as in 
all other similar instruments, is connected to the 
pointer, and may be constructed of several pieces of 
iron. The principle of its working is similar to that 
described above, in that the armature tends to set 
itself at right angles to the wire through which the 
current passes. This style of instrument is used where 
current is liable to flow in either direction. 

A simple form of meter for measuring current is 
shown in Fig. 82. Here we have an amperemeter 
which consists of a strip of copper fastened to a block 
of wood or other insulating material, as shown at A. 
A piece of magnetized steel, B, to which a needle, C, is 
attached, swings on a pivot or shaft which is suspended 
at the bridge D. A scale is provided from which the 
number of amperes flowing can be obtained. The 
needle is rigidly attached to the magnetized steel B and 
moves with it. The action of this instrument is as fob 
lows: When a magnetized piece of steel is brought near 
to a conductor through which a current of electricity 
is passing, the magnetized steel tends to set itself at 
right angles to the direction of the current. The 
stronger the current becomes, or the more highly mag- 
netized the piece of steel may be, the nearer to a posi¬ 
tion of right angles the armature will assume. It is 
not practical to use this construction of an instrument 
to cover a range of more than one-half of a right 


ELECTRICITY FOR ENGINBERS 


143 


angle, for when the needle moves through an angle of 
about 50 degrees, it will require a much greater 
increase of current in proportion to the movement to 
obtain the deflection and the additional degree of the 
indicating needle. Such an instrument as the above 
may also be used to determine the direction of flow of 



FIGURE 82 . 


current in a wire and is sometimes quite convenient on 
arc circuits which are liable to have their currents 
reversed either by wrong plugging of the board or the 
reversing of polarity in the dynamo. 

Voltmeters and ammeters used with alternating cur¬ 
rents must, of course, differ in some respects from 

% 


























144 


ELECTRICITY FOR ENGINEERS 


those employed for continuous currents. Alternation 
of the current does not permit the utilizing of the mag¬ 
netic effect of the current to the same extent or in 
exactly the same manner as continuous currents, but 
when the cores of magnets are built up of soft iron 
wires of small diameter, the resulting attraction 
between coil and core is similar, though not so strong 
as between a coil carrying direct current on a solid 
iron core. 

Another type of ammeter and voltmeter used with 
alternating or direct current is known as the hot wire 
instrument. A rather long, thin platinum wire is 
placed in the circuit and so arranged that its elonga¬ 
tion or expansion resulting from the heating effect of 
the current passing over it is made to operate a pointer 
mounted on a jeweled bearing. These instruments 
absorb but little current and are claimed to be per¬ 
manently correct. This class of instrument may be 
used on either direct or alternating current, and when 
used on alternating current the frequency or alterna¬ 
tions make no difference in the operation of the instru¬ 
ment. It is also unaffected by external magnetic fields, 
such as a neighboring dynamo or motor, and can be 
used close to a wire conducting current without being 
affected in its accuracy. When used as an ammeter it 
is connected in shunt with a resistance placed in the 
main circuit in the same manner as described for direct 
current ammeters, and in this way but a very small 
proportion of current is made to pass over the instru¬ 
ment. Separate resistances are also furnished with the 
instruments; so that by connecting these in series with 
the instrument they can be usod over a very wide range. 

Wattmeters. A few years ago, where current was 
sold by central stations to consumers, or in any other 


ELECTRICITY FOR ENGINEERS 


145 


place where it was desirable to measure the power fur¬ 
nished in the form of electricity, there were several 
kinds of differently constructed meters used to measure 
the amount of current. Some of these meters were 
based on the chemical action of the current; the current 
in passing to the work depositing metal from one plate 
to another. The plates or terminals of the meters 
were weighed before being placed in the circuit and 
again weighed on being taken out, the amount of metal 
having been deposited determining the amount of cur¬ 
rent used, as explained in the fore part of the book. 
Of late, however, most of the recording wattmeters in 
use are operated on the principle of the Thomson 
wattmeter. As has been explained under the definition 
of units, the work done (watts) is equal to the current 
(amperes) multiplied by the electromotive force (volts), 
or W = C x E. For a wattmeter to register correctly it 
must take a record of the volts and amperes. 

The Thomson wattmeter is simply a small motor in 
which the armature is used as a voltmeter and the 
fields as an ammeter. The armature is wound with fine 
wire and is connected to a small commutator made up 
of metal bars. Two very thin metal brushes bear on 
this commutator and carry the current to and from the 
armature. The armature is connected across the mains 
in just the same way as a voltmeter would be connected. 
The fields are wound with a coarse wire and are con¬ 
nected in series with the main circuit, thus acting as an 
ammeter. It can readily be seen that with the arma¬ 
ture influenced only by the voltage, and the fields by 
the current passing through the mains, the two acting 
together will correctly measure the power supplied. 
As the voltage rises or lowers, the speed of the arma¬ 
ture will be affected accordingly, and as the current 


146 


ELECTRICITY FOR ENGINEERS 


through the fields varies the electromagnetic effect 
produced by the fields and in which the armature 
revolves will vary, thus also varying the speed. By 
reference to Fig. 83, the fields F F are connected in 
series with one of the mains and the armature A is 



figure 83 . 


connected across the mains. Fig. 84 is a simplified 
diagram. Attached to the shaft on which the arma¬ 
ture rotates is a copper disc which revolves between 
the poles of a permanently magnetized steel magnet. 
Eddy currents are generated in this copper disc as the 















































ELECTRICITY FOR ENGINEERS 


147 


armature rotates, thereby acting as a brake against 
which the armature must work. Connected to the top 
of the shaft is a train work of wheels which move small 
pointers over the dials on the face of the instrument 
and record the amount of current which has passed 
through the meter. As no iron is used in either the 
armature or fields of the motor, the meter can be used 
on either alternating or direct current. 

In Fig. 85 we show a two wire meter with the case 
removed. 

In Fix. 86 a three wire meter is shown. 

Directions for Reading Meter Dials. To correctly read 
the sum indicated on the dial of a recording meter, the 



directions given herewith should be thoroughly under¬ 
stood and carefully followed. 

The figures (1,000, 10,000, etc.) under or over each 
dial refer to a complete revolution of the hand at that 
dial. 

Therefore, each division on the dial to the extreme 
right indicates not one, two, three, or four thousands 
of units, but one, two, three, or four hundreds of units. 

A complete revolution of the hand counts one thou¬ 
sand, and will have moved the hand on the second dial 
one division. Thus in reading Diagram No. 6, Fig. 
87 the first dial (that on the extreme right) indicates 
700, not 7,000. 








148 


ELECTRICITY FOR ENGINEERS 


A hand to be read as having completed a division, 
must be confirmed by the dial before it (to the right). 
It has not completed the division on which it may 
appear to rest, unless the hand before it has reached 



figure 85 . 


or passed o, or, in other words completed a revolution. 
For this reason it will be found easier and quicker to 
read a dial from right to left, as shown by reading Dia¬ 
gram No. 2, Fig. 87. 




































ELECTRICITY FOR ENGINEERS 


149 


The first dial (the extreme right) indicates 900. The 
second hand apparently rests on 0, but since the first 
rests only on 9 and has not completed its revolution, 



figure 86. 


the second dial also indicates 9. This 9, placed before 
the 900 already obtained, gives 9,900. 

This is also true of dial 3. The second hand, at 9, 
has not quite completed its revolution, so the third has 
not completed its division, therefore another 9 is 



































































150 


ELECTRICITY FOR ENGINEERS 


obtained, making 99,900. The same is true of dial 4, 
making 999,900. 

The last dial (the extreme left) appears to rest on 1, 
but since the fourth is only 9, the last has not com¬ 
pleted its division, and therefore reads o. The total 
reading is 999,900. 

The hands are sometimes slightly misplaced. In 
Diagram No. 8 the first diagram (the extreme right) 
reads o, which gives 000. The hand of the second 
dial is misplaced. As the first registers o, the second 
should rest exactly on a division; therefore it should 
have reached 8, making 8,000. The third hand is 
apparently on 3, but since the second hand is at 8, the 
third cannot have completed a division and must, 
therefore, indicate 2. The two remaining dials are 
correct, and make a total of 9,928,000. 

In Diagram No. 9, the second dial hand is mis¬ 
placed, for since the first indicates 1, the second should 
have just passed a division. As it is nearest to 8 it 
must have just passed that figure. The remaining 
three dials are approximately correct. The total indi¬ 
cation is 9,918,100. 

In Diagram No. 10, the second and fourth dial 
hands are slightly behind their correct position, but 
not enough to mislead in reading. The total indica¬ 
tion is 9,928,300. 

By carefully following these directions little diffi¬ 
culty will be found in reading the dial, even when the 
hands become misplaced. 

Note whether there is a constant marked on the 
dial. If there is, multiply the dial reading by the 
constant. With constant y 2y multiply by % \ that is, 
divide by 2. 

The “constant” of a meter is the term applied when 


ELECTRICITY FOR ENGINEERS 


151 


No.1 — 1.111.100 


No. 6 = 99.700 



o 



!)«* 0 «*S 0 N RECO^ 

WATT METER 

10000000 GENERAL ELECTRIC CO. ’°™ 

Watt HfS. Constant Watl Hrs.Q, 

No. 2 — 999,900 


o 


1000000 100000 10000 




o 



fo 


1000000 100000 


IOC 00 




( 5 s 


o 


rec or 0//Vc 

WATT METER 

loooooooQENERAL ELECTRIC CO. ,0 " 


Watt Hrs. 


^0**SON RECO« 0//V| 

WATT METER 

10000000 GENERAL ELECTRIC CO ,999 ^ 

vJ Watt Hrs. Constant Watl Hrsv_y 
^_ No.7 = 9.912.100 _ 

ioooooo looooo ioooo 




^ ort -SON Reco* 0//Vg 

WATT METER 


<5 


No. 3 —1.000,100 


1000000 100000 






av ,owson Rfco ft0//Vc ^ 

WATT METER 



iooooooogeneRAL ELECTRIC CO . 1000 

CJ Watt Hrs. Constant Watt Hrs. 1 Q , 

No.8 =9.928.000 

O 1000000 100000 




^o#s° N REC0 «0/ /Vc ( 

WATT METER 


• oooooooqenERAL ELECTRIC CO. ,00 ° 

iyWWatt Hrs. Constant Wan Hrs 

qJ 


10000000 GENERAL.ELECTRIC CO 1009 ^ 

iy Watt Hrs. Constant Watt Hrs. 1 <~Jj 


N 0 .4 =9.999.400 



No.9 = 9.918 100 


fn 

1000000 '100000 10000 

Ol 


fo 

1000000 *100000 10000 

0\ 




o 


REC 0 ^ 0//v 

WATT METER 

.oooooooGENERAL ELECTRIC CO. ,00 ° 


Watt Hrs- Constant Watt 


His.O 




'O 


No. 5 — 909.100 


1000000 100000 



o 


0 <WO#8° N REC0 ^0 //V<J 

WATT METER 

iooooooogeneRAL ELECTRIC CO. 1000 ^ 

Owatt Hrs. Constant Watt Hrs.v_/ 



1)^0**°" REC Of?0//VQ 

WATTMETER 

• oooooooGENERAL ELECTRIC CO. 1009 ^ 

C^Watt Hrs. Constant Watt Hrs.O^ 

No.10 = 9.928.300 

- ... " 

1000000 100000 10000 (^) 


fo 





lU+o«*o« *£ 00 * 0 ,^ 

WATT METER 

ioooooooqenERAL ELECTRIC CO. ,0 " 

Constant Watt Hrs.C_J 


l 

\QWatt Hrs. 


FIGURE 87. 






























152 


ELECTRICITY FOR ENGINEERS 


the meter is constructed to run at a lower speed than 
what would be necessary to measure the true number 
of watts which has passed through it. For instance, 
if the constant is 2 and the meter has registered 5,000 
watt-hours, then the meter having run only half as fast 
as it should, we multiply 5,000 by 2, which gives us 
10,000 watts as the actual amount that has passed 
through the meter. This scheme becomes necessary in 
order to register a large amount of current with a 
meter small in bulk or size. For convenience the 
maker often takes a 220 voltmeter which would read 
the number of watts direct on the dial at 220 volts and 
sells it fora no voltmeter by marking a constant on 
the dial of the meter. 


CHAPTER IX 


Arc Lamps. The principle on which the arc lamp oper¬ 
ates is shown in Fig. 89. Current is caused to flow 
from one carbon point to another through a space or gap 
between the carbons. The heat of the arc is sufficiently 
high to disintegrate the carbon and reduce it to a vapor, 
this vapor filling the space between the carbon points. 
The current passes over this space in a bow-shape path 
or arc, and it is from this fact that the lamp gets its 
name. The arc is constantly moving, and generally 
revolves around the carbon points. This can be easily 
seen by looking closely at a burning lamp through a 
smoked glass. After a lamp has been burning for 
some time on direct current the carbons assume the 
- shape shown in Fig. 88, the upper or positive carbon 
assuming a cup shape, while the lower carbon gener¬ 
ally burns to a point. This cup shape formation on 
the upper or positive carbon acts as a reflector to 
throw the light downward. The positive carbon burns 
away about twice as fast as the negative carbon and 
lamps must be trimmed accordingly. Sometimes the 
current feeding arc lamps (on direct current systems) 
becomes reversed, either through the dynamo reversing 
its polarity or through wrong plugging of the switch¬ 
board. The lamps will now burn “upside down,” or, 
in other words, the bottom carbon will be the positive 
one. In such a case, if let go, the carbon holders of 
the lamp will be burned and the lamp will burn for 
only half the time for which it was intended, owing to 
the fact that the lower or negative carbon is only one- 
half as long as the upper or positive carbon. Such a 

153 


154 


ELECTRICITY FOR ENGINEERS 


condition can be determined by either of the following 
ways: See if the light is being thrown downwards. 
See which carbon is burning away the faster. Raise 
the carbons and notice the formation of the carbon 
tips. When the carbons are separated it will be 
noticed that the tip of one carbon is considerably hot¬ 
ter than the other and is heated a longer distance from 
the point; this is the positive carbon. 



FIGURE 88. 

The action of the arc lamp used on direct current 
constant current systems is shown in Fig. 89. Current 
passes through wire T and over the coarsely wound 
solenoid M, thence down to the carbon, across the 
arc or crater, into the negative carbon and out again 
on the wire T\ The regulating action is as follows: 
A coil M', constructed of fine wire and of high resist¬ 
ance, is connected in shunt across the arc. The action 
of the current flowing through the solenoid M across 










ELECTRICITY FOR ENGINEERS 


155 


the crater or arc produces a magnetic pull on the 
solenoid core A and causes a separation of the car¬ 
bons. As these carbons burn away the resistance 
across the crater increases and a very small portion of 
the main current is caused to flow through the shunt 
coil M'. The magnetic pull of the shunt solenoid 
overcomes that of the series solenoid with the result 
that the solenoid core A is drawn into coil M' and the up¬ 
per carbon thus lowered, de¬ 
creasing the gap at the arc. In 
this way a constant regulation 
is going on, tending to keep 
the two carbons at a uniform 
distance apart. The upper car¬ 
bon rod is held by means of a 
clutch. When the carbons have 
burned away, so that the lower¬ 
ing of the solenoid does not 
lower them to the proper ex¬ 
tent, the clutch is released and 
the carbon drops, thus feeding 
the lamp. Some lamps are 
manufactured wherein the lower 
carbon is positive. This causes the light emitted from 
the crater to be projected upwards. The arc lamp 
frame is supplied with a shade on which the light cast 
from the arc is reflected downward. The advantage of 
this system is to obtain a better diffusion and distribu¬ 
tion of the light beneath the arc lamp. This lamp 
is not now generally used. 

Fig. 90 shows a diagram of connections for the 
improved Brush arc lamp. These lamps are used on 
constant current or series systems and their action is 
as follows: 




T'Q 


M 


Sri Us 


r*— 


M' 




tjn 3 . 

0 


FIGURE 89. 








































156 


ELECTRICITY FOR ENGINEERS 


The carbons should rest in contact when the lamp is 
cut out. When the switch is opened, part of the cur¬ 



rent from the positive terminal hook P goes through 
the adjuster to the yoke and thence through the carbon 






























































































































































ELECTRICITY FOR ENGINEERS 


157 


rod and carbons to the negative terminal hook N. 
The remainder of the current goes to the cutout 
block, but, as the cutout block is closed at first, the 
current crosses over through the cutout bar to the 
starting resistance, and so to the negative side of 
the lamp. A part of it, however, is shunted at the 
cutout block through the coarse wire of the magnets 
and so to the upper carbon rod and carbons and out. 
This shunted current energizes the magnet and so 
raises the armature which opens the cutout and at the 
same time establishes the arc by separating the car¬ 
bons. 

The fine wire winding is connected in the opposite 
direction from the coarse wire winding, and its attrac¬ 
tion is therefore opposite. When the arc increases in 
length, its resistance increases, and consequently the 
current in the fine wire is increased. The attraction of 
the coarse wire winding is therefore partly overcome 
and the armature begins to fall. As it falls, the arc is 
shortened and the current in the fine wire decreases. 
The mechanism feeds the carbons and regulates the 
arc so gradually that a perfect, steady arc is main¬ 
tained. 

The fine wire of the magnets is connected in series 
with the winding of a small auxiliary cutout magnet 
at the top of the mechanism. 

This magnet, which also has a supplementary coarse 
winding, does not raise its armature unless the voltage 
at the arc increases to 70 volts. The two windings 
connect at the inside terminal on the lower side of 
auxiliary cutout magnet, and the current from the fine 
wire of the main magnets passes through both wind¬ 
ings and then to the cutout block and so to the starting 
resistance and out, 


158 


ELECTRICITY FOR ENGINEERS 


If the main current through the carbon is interrupted 
(as by breaking of the carbons) the whole current of 
the lamp passes through the fine wire circuit. Before 
this excessive current has time to overheat the fine 
wire circuit, it energizes the auxiliary cutout mag¬ 
net, and closes a circuit directly across the lamp 
through the coarse wire on the auxiliary cutout to 
the main cutout block, and thence to the negative 
terminal. 

The auxiliary cutout operates instantly, and prevents 
any danger to the magnets during the short period 
required for the main armature to drop and throw in 
the main cutout. When the main cutout operates, the 
armature of the auxiliary cutout falls, because there is 
not sufficient current in that circuit to energize the 
magnet. 

The voltage at which the auxiliary cutout magnet 
operates depends on the position of its armature, 
which is regulated by the screw securing the armature 
in position. It should not be adjusted to operate at 
less than 70 volts. 

One of the three methods of suspension maybe used 
for Brush lamps. If chimney suspension, which is the 
most common, is adopted, the wire, cable or rope used 
to suspend the lamp must be carefully insulated from 
the chimney. For this purpose a porcelain insulator 
should be inserted between the support and the lamp, 
as shown in Fig. 91. 

Hook suspension may be used to advantage in some 
places, but great care must be taken to insulate the 
supporting wires from any conductors, as the hooks 
form the terminals of the lamps. 

The most convenient arrangement for indoor use is 
to suspend the lamp from a hanger board. The porce- 



ELECTRICITY FOR ENGINEERS 159 

lain base of the hanger board prevents short circuits 
or grounds. 

A protecting hood is not necessary for outdoor use, 
as the lamp chimney and its base are one casting and 
effectually exclude rain or 
snow water. 

The lamps run on circuits 
of 6.6 amperes for 1,200 and 
9.6 amperes for 2,000 nom¬ 
inal candlepower. In case 
it is necessary to run a lamp 
on a circuit differing from 
the standard, the lamp may 
be adjusted by moving the 
contact on the adjuster. 

About one ampere either 
above or below the normal 
may be compensated for by 
this means. 

Permanent adjustment for 
special circuits of variation 
greater than one ampere is 
made by filing the soft iron 
armature. The clutch should 
be so adjusted that the cen¬ 
ter of the armature is -ff in. 
above the plate when the trip 
on the first rod is touching 
the bushing, and jj in. when 
the trip on the second rod is in a similar position. 
A small gauge is convenient for adjusting the clutch. 
The position of the trip of the clutch determines the 
feeding point of the lamp. 

After thoroughly repairing and cleaning the lamp, it 



figure 91. 










160 


ELECTRICITY FOR ENGINEERS 


should be run a short time before installing. Lamps 
should not be tested in an exposed place, as a strong 
draft of air will cause unpleasant hissing which may be 
mistaken for some internal trouble. 

Lamps should not hiss or flame if good carbons are 
used. A voltmeter should always be used when adjust¬ 
ing or testing. 

The lamp terminals are marked P (positive) and N 
(negative) and should be connected into circuit accord¬ 
ingly. 

The carbons should be solid and of uniform quality. 
For the best results, the upper carbon should be 
12 in. x T \ in., and the lower 7 in. x T 7 6 - in. The stub 
of the upper carbon may then be used in the lower 
holder when retrimming. 

At each trimming the rod should be carefully wiped 
with clean cotton waste. If any sticky or dirty spots 
appear, which cannot be readily removed with waste, 
use a piece of well-worn crocus cloth, always being 
careful to use a piece of clean waste before pushing 
the rod into the lamp. It should never be pushed up 
into the lamp in a dirty condition. 

The carbon rod may be unscrewed and removed by a 
small screw driver or small strip of metal inserted in 
the slot cut in the rod cap. The cap will remain in 
the hole through the yoke when the rod is taken 
out. 

In Fig. 92 an interior view of the Thomson-Houston 
arc lamp is shown. This lamp is also used on con¬ 
stant current systems. 

The lamps should be hung from the hanger boards 
provided with each lamp, or from suitable supports of 
wire or chain. 

As the hooks on the lamp form also its terminals, 


ELECTRICITY FOR ENGINEERS 161 

they should be insulated, where a hanger board is not 
used, from the chains or wires used to support the 
lamp. 



figure 92. 

When the lamps are hung where they are exposed to 
the weather, they should be covered with a metal 
hood, to prevent injury from rain and snow. 






162 


ELECTRICITY FOR ENGINEERS 


In such cases, care should be taken that the circuit 
wires do not form a contact on the metal hood and 
short circuit the lamp. 

Before the lamps are hung up they should be care¬ 
fully examined to see that the joints are free to move, 
and that all connections are perfect. 

No lamp should be allowed to remain in circuit, 
with the covers removed and the mechanism exposed. 
Such practice is dangerous, and in violation of insur¬ 
ance rules. 

The object of testing the lamps in the station is to 
find any defects, if such exist, and to test all the con¬ 
ditions of running before delivering them to custom¬ 
ers. The lamps should not be hung up in their 
respective places in the external circuit, until every¬ 
thing is running with perfect satisfaction. 

The tension of the clamp which holds the rod is 
adjusted by raising or lowering the arm at the top of 
the guide rod. (See Fig. 93.) If the tension is too 
great the rod and clutch will wear badly and the feed¬ 
ing will be uneven, causing unsteadiness in the lights. 
Too little tension will not allow the clutch to hold up 
the rod and any sudden jar to the lamp will cause the 
rod to fall and the light to go out. 

The double carbon, or M lamp, should have the ten¬ 
sion of the second carbon a trifle lighter than the first 
one. 

When adjusting the tension, be sure to keep the 
guide rod perpendicular and in perfect line with the 
carbon rod; it should be free to move up and down 
without sticking. 

The tension of the clutch in the D lamp should be 
the same as that of the K lamp. It is adjusted by 
tightening or loosening the small coil spring from 


electricity Eor engineers 


163 


the arm of the clutch to the bottom of the clamp 
stop. 

To adjust the feeding point in the K lamp, press 
down the main armature as far as it will go, then push 



up the rod about one-half its length, let go the arma¬ 
ture and then press it down slowly and note the dis¬ 
tance of the bottom side of the armature above the 
base of the curved part of the pole. When the rod 
















































































































164 


ELECTRICITY FOR ENGINEERS 


just feeds, this distance should be in. If it is not, 
raise or lower the small stop which slides on the guide 
rod passing through the arm of the clutch, until the 
carbon rod will feed when the armature is % in. from 
the rocker frame at base of pole. 

To adjust the feeding point of the M lamp, adjust 
the first rod as in the K lamp. Then let the first rod 
down until the cap at the top rests on the transfer 
lever. The second rod should feed with the armature 
at a point T V in. higher than it was while feeding the 
first rod, that is, it should be fa in. from rocker frame 
at base of pole. 

The feeding point of the D lamp is adjusted by slid¬ 
ing the clamp stop up or down, so that the rod will 
feed when the relative distances of the armature of the 
lifting magnet and the armature of the shunt magnet 
from rocker arm frame are in the ratio of I to 2. 
There should be a slight lateral play in the rocker, 
between the lugs of the rocker frame. 

The armatures of all the magnets should be central 
with cores, and come down squarely and evenly. 
There should be a separation of fa in. between the sil¬ 
ver contact points, when the armature of the starting 
magnet is down. This contact should be perfect when 
the armature is up. The arm for adjusting the tension 
should not touch the wire or frame of the lamp when 
at the highest point. There should be a space of fa in. 
or }£ in. between the body of the clutch and the arm 
of the clutch, to allow for wear on the bearing surfaces. 

Always trim the lamp with carbons of proper length 
to cut out automatically, that is, have twice as much 
carbon projecting from the top as from the bottom 
holder. Always allow a space of in., when the lamp 
is trimmed, from the round head screw in the rod, near 


ELECTRICITY FOR ENGINEERS 


165 


the carbon holder, to the edge of the upper bushing, so 
that there will be sufficient space to start the arc. 

The arcs of the 1,200 candlepower lamps should be 
adjusted to g 3 T in., with full length of carbon. Arcs of 
2,000 candlepower lamps should be adjusted from tV 
to in. when good carbons are used. 

The action of a lamp that feeds badly may often be 
confounded with a badly flaming carbon. The distinc¬ 
tion can readily be made after a short observation. 
The arc of a lamp that feeds badly will gradually grow 
long until it flames, the clutch will let go suddenly, the 
upper carbon will fall until it touches the lower carbon, 
and then pick up. A bad carbon may burn nicely and 
feed evenly until a bad spot in the carbon is reached, 
when the arc will suddenly become long and flame and 
smoke, due to impurities in the carbon. Instead of 
dropping, as in the former case, 
the upper carbon will feed to its 
correct position without touching 
the lower carbon. 

In a series arc lamp the shunt 
coil is used to regulate the voltage 
over the arc. With constant po¬ 
tential arc lamps this shunt coil 
is not needed, owing to the fact 
that the voltage over the lamp 
is practically constant. Fig. 94 
shows a diagram of an arc lamp 
for use on constant potential cir¬ 
cuits. The upper carbon is sup¬ 
ported by means of an iron yoke 
which forms a core to the two 

solenoids M M. Current entering binding post T 
passes through the windings of these two solenoids and 



FIGURE 94. 




































166 


ELECTRICITY FOR ENGINEERS 


then through the carbons and through the resistance 
coil R to the other terminal of the lamp. The action 
of the lamp is as follows: Current passing over the 
solenoids M M is regulated by the resistance across 
the arc. This current produces an electromagnetic 
pull on the iron core and floats, magnetically, the core 
and upper carbon. When the carbons burn away at 
the crater the distance from point to point of the car¬ 
bons is increased and a corresponding increase in 
resistance to the flow of the current takes place. This 
reduces the flow of current around the solenoids and 
correspondingly reduces the electromagnetic pull on 
the core; the iron core and carbon fall a slight dis¬ 
tance by gravity. In so doing the distance at the 
crater is decreased and the flow of current increased, 
thus increasing the flow of current around the solenoids 
and drawing up the core and carbons. In this way a 
very nice equilibrium between gravity and magnetic 
pull is maintained. It will be noticed that this lamp 
has no automatic cutout as has the constant current 
arc lamp. In a series arc lamp when the carbons are 
all consumed, the automatic cutout closes the circuit 
from the positive and negative binding posts of the 
individual arc lamp, thereby maintaining a path 
through the arc lamp over which the current can con¬ 
tinue to flow to supply the remaining arc lamps in the 
series circuit. 

The series arc, as its name would indicate, is the 
most simple of all lighting circuits. The lamps are 
arranged so that all the current from the positive pole 
of the dynamo goes through each, and from the last on 
the conductor leads back to the dynamo. The series 
system is more generally used where it is desired to 
illuminate a large district, as in street lighting. It is 


ELECTRICITY FOR ENGINEERS 


167 


also used to some extent in store lighting, although the 
series arc is fast being replaced with the constant 
potential arc for this purpose. 

In the low tension or constant potential arc lamp the 
use of a cutout mechanism is not necessary, because 
these lamps burn singly across the system of wiring, 
where a constant potential is maintained, and hence 
when the carbons are all consumed, current simply 
ceases to flow across them. In the open arc lamp the 
potential across the crater is usually from 45 to 50 
volts, while in the inclosed arc lamp the potential 
across the crater is from 68 to 75 volts. This is due to 
the increased resistance through the crater, because of 
the peculiar nature of the gases emitted from the 
crater burning in a condition with practically no atmos¬ 
phere. When such an arc lamp is connected across a 
no volt circuit, the lamp contains a resistance coil in 
the mechanism box over which the current must flow 
before producing the arc, R (Fig. 94). This resistance 
coil assists to reduce the pressure from no volts down 
to the pressure required by the arc or crater. If, for 
instance, the electromotive force across the wires 
supplying current to a low tension arc lamp is no 
volts and the pressure required to maintain the arc or 
crater is 70 volts, then the resistance coil chokes down 
the electromotive force from no to 70, or 40 volts. If 
the arc consumes 4 amperes of current then the loss is 
4 (amperes) times 40 (volts); or 160 watts. This 160 
watts is lost by heat radiating to the atmosphere from 
the wire of the resistance coil. The constant potential 
lamp is usually referred to as the low tension arc lamp. 
The high tension arc lamp generally burns with the arc 
in the open air, while the low tension lamp burns with 
the arc encased in a small glass bulb so arranged as to 


168 


ELECTRICITY FOR ENGINEERS 


permit the upper carbon to slide into the bulb in a 
manner that will maintain, as near as possible, a condi¬ 
tion whereby the arc burns in a gas containing no 
oxygen. The enclosed arc lamp has the advantage of 
burning a considerable number of hours without being 
recarboned or trimmed; but it also has the disadvantage 
that the bulb enclosing the arc turns black after burn¬ 
ing for some time, caused by the gases emitted from 
the arc. This renders the bulb partially opaque, 
consequently imprisoning a considerable quantity of 
useful light. Enclosed arc lamps are also operated in 
series systems, and where they are so used the objec¬ 
tion of loss due to the cutting down of the voltage (as 
in constant potential lamps) is overcome. Enclosed 
lamps are also operated on alternating current systems. 

The operation of the alternating arc lamp and the 
mechanism in the lamp is very similar to that of the 
direct current arc lamp, but the magnets instead of 
being constructed of solid iron, are laminated in a 
similar manner as the system of lamination explained 
in the construction of armatures. These laminated 
cores and other parts forming the magnetic circuit 
in the arc lamp are necessary to avoid eddy cur¬ 
rents. The crater has neither a cup shape on the 
upper carbon nor a point on the lower carbon, because 
current flows through the crater alternately positive 
and negative with each alternation. In the alternating 
arc lamp the upper and lower carbons burn away with 
almost equal rapidity, and the same quantity of light 
is projected upward as downward. 

In Fig. 95 is shown an arc lamp with case removed. 
The two upper coils are the coarsely wound series 
coils, while the two lower coils are the finely wound 
shunt coils. This lamp is adapted for an enclosed arc 


ELECTRICITY FOR ENGINEERS 


169 


bulb. The magnetically attracted cores are U shaped, 
and both cores are connected together mechanically by 
non-magnetic metal, such as brass or zinc, so that the 
magnetism set up in the shunt coils will not be affected 
by the magnetism set up by the 
series coils. This scheme is used in 
alternating current lamps, while in 
direct current lamps the cores are 
made of H shaped iron not lami¬ 
nated. 

In Figs. 96 to 98 are shown three 
views of series enclosed alternating 
current arc lamps of the Western 
Electric Company. 

Fig. 96. Side view of lamp, show¬ 
ing one series and one shunt spool, 
lever movement and adjusting 
weight. This weight is fastened 
upon a threaded rod, and the finest 
adjustment can be obtained by 
screwing the weight backward or for¬ 
ward. Threads can be clamped in 
position when the correct adjustment 
is obtained. 

Fig. 97. Front view of lamp, show¬ 
ing shunt spools, supporting resist 
ance and cutout. Note that lever figure 95 
carries no current when in normal 
working position, but that insulated bridge forms con¬ 
nection across two contacts, completing cutout circuit 
when in position shown in cut. 

Fig. 98. Rear view of lamp, showing series spool, 
short circuiting switch and manner of suspending dash 
pot. Note that the dash pot is inverted, allowing such 







170 


ELECTRICITY FOR ENGINEERS 


dirt as may accumulate therein to fall out rather than 
in the dash pot. 

The three cuts show the manner of suspending the 
spools and their accessibility, it being possible to 
remove any spool by simply taking out the two screws 



FIGURE 96 . FIGURE 97 . FIGURE 98 . 




which fasten it to the frame, and lifting it off the 
lower support. 

The carbons used in arc lamps are extremely hard 
and dense. They are made from a mixture of pow¬ 
dered gas house coke, ground very fine, and a liquid 
like molasses, coal tar, or some similar hydro-carbon, 
forming a stiff, homogeneous paste. This is molded 






ELECTRICITY FOR ENGINEERS 


171 


into rods or pencils of required size and length, or 
other shapes, being solidified under powerful hydro¬ 
static pressure. The carbons are now allowed to dry, 
after which they are placed in crucibles or ovens, 
thoroughly covered with powdered carbon, either lamp¬ 
black or plumbago, and baked for several hours at a 
high temperature. After cooling, they are sometimes 
repeatedly treated to a soaking bath of some fluid 
hydro-carbon, alternated with baking, until the product 
is dense as possible, all pores and openings having 
been filled solid. Arc carbons are often plated with 
copper by electrolysis, to insure better conductivity. 

It is said that one 2,000 candlepower arc lamp will 
light in open yards 20,000 sq. ft.; in railroad stations, 
14,000 sq. ft.; in foundries and machine shops, 5000 
to 2,000 sq. ft. Where good, even illumination is 
desired, it is advisable to use a greater number of 
smaller lamps evenly distributed. 


CHAPTER X 


Incandescent Lamps. As nearly every one is familiar 
with the construction of the incandescent lamp no 
detailed description will be undertaken, suffice it to 
say that the incandescent lamp comprises a carbon 
filament enclosed in a glass bulb from which the air 
has, as far as possible, been withdrawn, the carbon 
filament being soldered to the ends of small platinum 
wires entering the glass shell. Incandescent lamps can 
be burned either in series or in multiple; the multiple 
system being the most used. Series incandescent 
lamps are used to a considerable extent in the smaller 
towns for street lighting and also for the small minia¬ 
ture lamps burned in series on a constant potential sys¬ 
tem and used for decorative purposes. They are also 
used in street car lighting. 

When incandescent lamps are to be used in series, 
they should be carefully selected; there is quite a 
difference in the current consumed by different lamps, 
even of the same make, and when they are all limited 
to the same current quite a difference in candlepower 
may be noticeable. Some will be above their rated 
candlepower and others below. 

The resistance of an incandescent lamp when cold is 
very high, varying in the ordinary 16 candlepower no 
volt lamp from 600 to 1,000 ohms. When the lamp 
becomes heated, as when current is passing through it, 
the resistance reduces considerably, being in the 16 
candlepower no volt lamp about 220 ohms. 

The current required by the various incandescent 
lamps varies considerably for lamps of the same volt- 

172 


O'Wn-fc* OJ to 


ELECTRICITY FOR ENGINEERS 


173 


age and candlepower, but a good average which can be 
used in figuring currents is ampere for a 16 candle- 
power iio volt lamp and % ampere for the 220 volt 
16 candlepower lamp. The amount of power, in watts, 
consumed by a lamp is equal to the voltage multiplied 
by the current, or W = C x E. A 16 candlepower no 
volt lamp taking ^ ampere would consume no x 
^ = 55 watts, while a 220 volt lamp taking ampere 
would consume 220 x % = 55 watts. It will thus be 
seen that while the current and voltage may vary, the 
amount of power consumed will be approximately the 
same for all 16 candlepower lamps. Lamps are rated 
at a certain number of watts per candle, the amount 
varying from 3 to 4 watts for 16 candlepower no volt 
lamps. The proper lamp to be used varies according 
to the conditions. While less power is consumed in 
a 3.1 watt lamp, the life of the lamp is comparatively 
shorter, so that the lamps will have to be renewed 
oftener. With a 4 watt lamp a greater amount of cur¬ 
rent is consumed, but the life of the lamp is longer. 
Another point of great importance in burning incan¬ 
descent lamps is the voltage. The table below shows 
what effect variation in voltage has on the candlepower 
and efficiency. 

An increase in voltage increases the candlepower. 
This increases the efficiency and shortens the life as 
follows: 

A lamp burning at— 


Normal voltage gives ioo per cent. C. P. and consumes 3-i Watts per C. P. 


1 per cent, above normal gives 106 per cent. C 


112 


4» 44 44 

44 

“ 118 “ “ 



11 

2.8 

44 44 44 

44 

“ 125 “ “ 



• 4 

2.7 

44 44 44 

4 4 

“ 132 “ “ 



* * 

2.6 

44 44 44 

44 

“ 140 “ “ 



4 4 

2.5 


P. and consumes 3 . Watts per C. P. 


2.9 


44 
t i 


A lamp burning at normal voltage should give its 


















174 


ELECTRICITY FOR ENGINEERS 


full candlepower at its rated efficiency. A 3.1 watt 
lamp burning below its voltage loses its efficiency and 
candlepower as follows: 

If burned— 


1 per cent, below normal it gives 95 per cent.C. P. and consumes 3.2 Watts per C 


2 

3 

4 

5 

6 
10 


9° 

85 

80 

75 

70 

5o 


3-35 

3-5 

3-6 

3- 75 

4 - 
4.6 


By referring to the table it will be seen that with the 
voltage raised 3 per cent, (on a no volt system to a 
little over 113 volts) the candlepower will increase 18 
per cent., or in other words, a 16 candlepower lamp 
would be raised to nearly 19 candlepower. At the 
same time raising the voltage will decrease the life of 
the lamp. This is shown in the following table where, 
with an increase of 6 per cent, in the voltage, the life 
of the lamp is reduced 70 per cent. A lamp at normal 
voltage has 100 per cent. life. 


The same lamp i per cent, above normal loses 18 per cent. life. 


2 

3 


3o 

44 


4 

5 

6 


t ( 
(t 


(( 


i i 


55 “ 
62 “ 
70 “ 


To obtain satisfactory results, the voltage should be 
kept constant at just the proper value. 

Considerable heat is generated in an incandescent 
lamp, so that as a general rule it is a bad plan to use 
paper shades which come very close to the bulb. 
Where lamps are hung so that there is a liability of 
their coming in contact with surrounding inflammable 
material, such as in warehouses and store-rooms, it is a 
good plan to enclose the lamp in a wire guard. 

The following table will prove a handy reference for 
estimating the number of lamps (8 to 50 C. P.) that 
can be run per horsepower or kilowatt. The table is 



































ELECTRICITY FOR ENGINEERS 


175 


figured for theoretical values, so that the actual horse¬ 
power or kilowatts delivered must be used, or else 
values less than those given must be used to allow for 
loss in the lines. 


Candle-power. 


8 

8 

16 

16 

16 

16 

p,o 

20 

20 

25 

25 

25 

25 

32 

32 

32 

50 

50 

50 


Efficiency. 


3-5 

4 

3 

3 -i 

3-5 

4 
3 

3-1 

3-5 

3 

3 -i 

3-5 

4 
3 

3-1 

3-5 

3 

3 -i 

3-5 


Total Watts. 


28 

32 

48 

50 

56 

64 

60 

62 

7 o 

75 

77-5 

87.5 

100 

96 

99.2 

112 

150 

155 

175 


Per 

Horsepower. 


26.6 

23-3 

15.5 
14.9 

13.3 

11 .6 

12.4 
12 

10.6 

9-9 

9.6 

8-5 

74 

7 

7-5 

6.6 
4.9 
4-8 
4-2 


Per Kilowatt. 


35-7 

31.2 

20.8 
20 

17.8 

156 

16.6 

16.1 

14.2 

13.3 

12.9 

11.4 

10 

10.4 
10 

8.9 

6.6 

6.4 

5.7 


The first column gives the candlepower. The second 
column gives the number of watts consumed for each 
single candlepower obtained, and is called the effi¬ 
ciency of the lamp. Multiply the total candlepower 
by the efficiency and you get the total number of watts 
consumed by the lamp. The fourth column shows the 
number of lamps per 746 watts, and the last column 
the number of lamps per 1,000 watts. 

The current and watts consumed by no volt lamps 
of the different candlepowers are approximately given 
below. 


4 candlepower.0.18 amperes, 20 watts 

8 “ .0.29 “ 32 



















176 


ELECTRICITY FOR ENGINEERS 


The light given off by an incandescent lamp varies 
according to the position from which it is viewed. In 
some makes of lamps most of the light is given off 
directly downward, while in other lamps the maximum 
light is given off in a horizontal direction. The best 
lamp to use must be determined by the location of the 
lamp and the place where the light is required. By 
the use of suitable reflectors or shades the light can be 
thrown in any direction desired. A 16 candlepower 
lamp if placed seven feet above the floor will light up 
a floor space of 100 sq. ft., providing the walls are of a 
light color. If the walls are of a dull color, or if a 
bright illumination is desired more lamps should be 
used. Glass globes placed over the lamps reduce the 
light to a considerable extent, as is shown in the fol¬ 
lowing table: 

Clear glass.io per cent. 

Holophane.12 “ 

Opaline .20 to 40 “ 

Ground.25 to 30 “ 

Opal .25 to 60 “ 







CHAPTER XI 


The Nernst Lamp. Very recently a new type of elec¬ 
tric lamp has been introduced which has a few charac¬ 
teristics of the arc lamp and many of the characteristics 
of the incandescent lamp. It is a lamp that can be 
successfully operated only on alternating currents. 
That part of the lamp from which the light is emitted 
is called the glower. The glower performs about the 
same functions as does the filament in an incandescent 
lamp. 

In Fig. 99 a diagram of a six glower lamp is shown. 
The six glowers are shown at 6. These glowers are in 
the shape of small rods and are composed of an oxid 
which, at the normal temperature, is of very high 
resistance, the resistance being so high that practically 
no current can flow through them. When these rods 
become heated, the resistance reduces considerably, so 
that they will conduct current. The heaters which are 
composed of a considerable length of fine platinum 
wire embedded in porcelain, are shown at 5. The 
action of the lamp is as follows: Current enters at 1, 
and being unable to flow over the glowers on account 
of their high resistance, passes to the cutout 4', then 
through the platinum wire of the heaters back to the 
other side of the cutout 4. As the platinum wire in 
the heaters becomes heated, the glowers, which are 
placed directly below them, also heat up and in time 
their resistance becomes so reduced that current will 
pass through them. The current will now pass through 
the glowers to what is known as the ballast, 7. This 

177 


178 


ELECTRICITY FOR ENGINEERS 


ballast is composed of fine iron wire and its purpose is 
to steady the current through the glower. From the 
fact that iron wire increases in resistance with increase 
of current, this wire acts as a regulator, tending to cut 


6 



FIGURE 99 . 


✓ 



down any fluctuations in the current strength. It will 
be noticed that there is a separate ballast for each 
glower. From the ballast the current flows around the 
coil of wire 3. Inside of this coil is an iron core which 


































































































ELECTRICITY FOR ENGINEERS 


179 


moves up and down, and connected to the lower end 
of this core are the cutouts 4,4'. As the glower 
becomes heated, more current is sent around this coil, 
until it becomes of such strength that the core is 
drawn in, thus opening the cutouts. All of the cur¬ 
rent will now flow through the glowers. The Nernst 
lamp does not operate successfully on direct current, 




FIGURE 100 . FIGURE 101 . 

due to the blackening of the glower caused by decom¬ 
position of the platinum contacts with which they are 
connected. These lamps are made in sizes of from I 
to 30 glowers, and they consume about 88 watts per 
glower. The light resembles very closely the light 
from a Welsbach gas burner, although the green tinge 
of the Welsbach is not present. 





180 ELECTRICITY for engineers 

In Fig. ioo is shown the single glower lamp 
assembled, which can be inserted in an ordinary Edi¬ 
son socket. 

In Fig. ioi the six glower lamp, with dome attached, 
is shown. 


CHAPTER XII 


Line Testing. In the operation of electric light and 
power circuits three principal causes of trouble are 
continually encountered. These are the open circuit, 
the short circuit, the ground, and also combinations of 
these, as there is nothing which prevents the existence 
of all three defects on any line at the same time. In 
order to study these properly, let us refer to Fig. 102, 
which shows an ordinary incandescent circuit equipped 
with the necessary cutout and a switch. 

An open circuit may be caused by poor contact, or 



figure 102. 


failure to make any contact at all, of the fuse. If this 
is the cause, the light can be made to burn by connect¬ 
ing the fuse terminals A and B or C and D by means 
of short pieces of wire. Such wire must, however, be 
used only for an instant to make sure of the trouble, 
and proper fuses must then be provided. Another 
method of locating an open circuit in the fuse consists 
of moistening the finger tips and placing the tips of 
two fingers of the same hand on B and D. If the fuses 
are in order, a slight shock will be felt; this method is 
applicable only on low voltage systems and must never 

be used where the voltage exceeds 250. 

181 














182 ELECTRICITY FOR ENGINEERS 

If the fuses are found all right, the next place to look 
for the cause of an open circuit is at the switch. The 
contact points of switches are often so badly burned 
or covered with dirt and grease that they do not make 
proper connection and hence the lights will not burn. 

The switch can be tested with the fingers just as we 
tested the cutout, and if the shock is felt the line is 
all right to this point. In testing the switch, be sure 
you test at the proper point (i and 2) in the figure 
which shows a switch, the blades of which cross. 
Some switches make connection straight along without 
crossing. In testing with a wire, as shown above, be 
very careful not to connect the points 1 and 2 at the 
switch, or you will have a short circuit. 

If the line is found alive at the far side (points I and 
2) of the switch shown, and still the lights do not burn, 
it is quite likely that there is a broken wire between 
the switch and the lamps. This break in the wire is 
not always visible, as often the wire is entirely con¬ 
cealed, and even when the wire is in plain view, the 
break may extend only to the copper and leave the 
outer insulation apparently perfect. 

If we are dealing with concealed wires that appear 
only where the lights are connected, we must first 
examine the connections at all such places and see 
whether they are in good order. If we find nothing 
wrong there we may proceed to locate our open circuit 
(which we shall assume to be at E) by the following 
method: In place of one of the fuses AB or CD, con¬ 
nect any incandescent lamp (if plug cutouts are used 
the lamp can be screwed in instead of the plug). Now 
connect a wire from 1 or 2 of the switch to 3 or 4 of 
the nearest lamp. 

If we happen to connect our wire from 1 to 4 we 


ELECTRICITY FOR ENGINEERS 


183 


shall make a short circuit and the lamp at the cutout 
will burn at full candlepower, but none of the other 
lamps will burn at all. Now disconnect the test wire 
from 4 and connect it at 3; if the broken wire is at E, 
as we have assumed, all the lights will now burn in 
series with the lamp in the cutout. If there are but 
few lights connected in the circuit, this lamp will burn 
at about half candlepower; if there are many lamps 
connected it will come nearly to full candlepower, and 
the lamps in the circuit will show nothing. 

If instead of an open circuit the cause of our trouble 
is a short circuit, it will first make itself evident by a 
burned out fuse in the cutout at AB or CD. 

A little experience will soon enable one to judge 
whether a burned out fuse is due to an overload or a 
short circuit; the damage to terminals and the evi¬ 
dence of burning will be much greater from a “short” 
than from a slight overload. 

Often the current that “blows” the fuse will also 
burn out the wire which caused the “short,” so that 
the line will seem perfectly clear when a new fuse is 
inserted. 

If an inspection of the wires and apparatus does not 
reveal the location of the trouble, we may fuse up one 
side of the circuit and connect an incandescent lamp 
in place of the other fuse. If the “short” is still on, 
the lamp will burn at full candle power. 

A short circuit may consist of anything of low elec¬ 
trical resistance that brings the wires of opposite 
polarity into electrical connection with each other. 
Thus, if the two points, F and G, although several 
hundred feet or even yards apart, were in connection 
with gas or water piping of low electrical resistance, 
all current would flow through the piping from F to G, 


184 


ELECTRICITY FOR ENGINEERS 


and there would be none to flow through the lamps. 
Short circuits are also often caused by small wires in¬ 
side of sockets or fixtures coming in improper contact. 
In one instance a short circuit which caused a search 
of several hours was finally located in the butt of an 
Edison base lamp, the center contact piece of which 
had been put on crooked in such a manner that when 
the lamp was screwed into its socket this center piece 
made connection with opposite poles within the socket. 

If a careful examination does not reveal the “short” 
it will be necessary to cut the wires, say at H; if this 
clears the line so that all lamps nearer the cutout than 
H burn, the trouble must be beyond H; if not, the line 
must be cut again nearer the cutout until finally the 
exact location of the trouble is found. 

Any connection of any part of an electrical circuit to 
earth is called a “ground,” and wires so connected are 
said to be grounded. One ground on a system will 
not necessarily do much harm or interfere with the 
operation of the system. It will, however, greatly 
increase the probability of electric shocks to people 
coming in contact with any part of the wiring. Also, 
if there is a ground on one side of a system, the 
appearance of a second ground on the other side of the 
system will be equal to a short circuit, if both are of 
low resistance, and probably cause the burning out of 
fuses or wires. 

If a ground is of high resistance, it may merely 
waste energy through leakage of current; or it may 
cause slow destruction of a wire or sometimes a gas or 
water pipe by electrolytic action. Aside from direct 
contact with metal parts of buildings, the most prolific 
cause of grounds is found in dampness. 

Grounds may be located by means of the Wheatstone 


ELECTRICITY FOR ENGINEERS 185 

bridge, magneto or a common bell and battery. After 
removing the fuses from the grounded part of the 
system, connect one side of the apparatus to a good 
ground, such as a water pipe, and the other side to the 
system. Proceed in the same way as explained for 
short circuits; that is, cut the lines until the ground is 
located, or the line shows clear. Where the wiring is 
concealed and there are a number of switches control¬ 
ling chandeliers, grounds can very often be located by 
switching off one fixture at a time, for when the 
grounded fixture is switched off the line will show 
clear. 

. To facilitate the discovery of grounds as soon as they 
come on, most switchboards are equipped with ground 
detectors of some kind. 

The cheapest and easiest to install of these consists 
of two lamps in series, as shown in Fig. 103. So long 



figure 103 . 


as both sides of the system are clear of grounds, the 
lamps will both burn at equal candlepower (rather dim) 
no matter whether the buttom C be pressed or not. 
But should a ground come on the -f wire, say at B, and 
the button C be then pressed, the lamp 2 will be 
deprived of current and lamp 1 will burn at full candle- 
power. In such a case the current passes from the 
+ wire to the ground B, through the ground to C, 
















186 


ELECTRICITY FOR ENGINEERS 


button C and lamp I to the - wire. Should a ground 
come at A, lamp I would be cut out and 2 would 




o 


w 

« 

p 

o 

PH 


burn at full candlepower. The great disadvantage of 
the lamp ground detector lies in the fact that it is not 
very sensitive; that is, unless the ground is of quite 

























ELECTRICITY FOR ENGINEERS v 187 

low resistance the difference in the brilliancy of the 
lamps will hardly be noticeable. 

A much more satisfactory arrangement is that shown 
in Fig. 104, where a voltmeter is connected for that 
purpose. With the two single pole switches A and B 
in the position shown, the voltmeter indicates the 
pressure of the dynamo; if B is thrown over, the 
current from the -f wire passes through the voltmeter 
to the ground, and if there is a ground on the - wire it 
will indicate it. If B is thrown back and A over, a 



ground on the + wire will be indicated. If the system 
is perfectly clear, the voltmeter will indicate nothing 
with either one of the switches thrown over. This test 
of lines and circuits should be quite frequently made. 

Testing Efficiency of Dynamos and Motors. The simplest 
means of testing the efficiency of motors is shown in 
Fig. 105. 

This is known as the Prony brake, and consists of a 
pair of clamps arranged for thumb screws and fastened 
to the pulley of the motor, and a set of scales. 

We will assume that we are testing the efficiency of 






















188 


ELECTRICITY FOR ENGINEERS 


a motor. We will arrange the clamps over the pulley 
as shown in the figure and on the long end of the 
clamp we will arrange a bolt, from which we may 
impart the pressure obtained to the platform of a pair 
of scales. In the circuit supplying the motor with cur¬ 
rent we will connect an amperemeter and a voltmeter. 
We will now start the motor and press down on the 
clamps by means of the thumb screw, until the 
mechanical energy expended is sufficiently high to 
cause the desired consumption of current shown by the 
amperemeter at the pressure shown by the voltmeter. 
With a tachometer or speed indicator we will find the 
number of revolutions of the motor per minute. When 
this has been done, we will take the weights on the 
scales and balance the pressure brought down on the 
platform. Now stop the motor. The weight indi¬ 
cated by the scales is that weight which the motor 
would have revolved through a circle, the radius, or 

half the diameter of which is the distance from the 

% 

center of the motor shaft to the center of the bolt 
pressing on the scale platform, Fig. 105. To find the 
horsepower exerted, multiply the distance between the 
bolt and the armature shaft by 2. This will be the 
diameter of the circle described. Multiply this by 
3.1416. This will be the circumference of the circle 
described. Multiply this by the number of pounds 
indicated by the scales, multiply this by the number of 
revolutions per minute, and divide the answer by 
33,000. 

Suppose your amperemeter registered 50.9 amperes 
and your voltmeter registered no volts. This would 
be 50.9 x 110 = 5,599 watts consumed. Divided by 746 
watts, the electrical horsepower would be 7^ horse¬ 
power consumed, 


ELECTRICITY FOR ENGINEERS 


189 


Suppose the dynamometer proved that you obtained 
six actual mechanical horsepower. Then 6 divided by 
7/^ would be 8o per cent, efficiency which the motor 
would have for changing electrical energy into mechan¬ 
ical energy. 

To test the efficiency of a dynamo we must first find 
how much power is being delivered to it by the engine. 
This is done in the usual manner by means of the indi¬ 
cator, etc. Having obtained this, it is simply neces¬ 
sary to connect an ammeter and voltmeter and, taking 
simultaneous readings of both, find the power given 
out by the dynamo by multiplying together the volts 
and amperes. 

As an example, suppose we have found that our 
engine is delivering 40 H. P. while we are obtaining 
from our dynamo 200 amperes at no volts pressure. 
200 x no divided by 746 will give us the electrical 
energy we are receiving; in this case a trifle less than 
29.5 H. P. To find the efficiency of the dynamo we 
divide the power received from the dynamo by that 
delivered to it by the engine, 29.5 divided by 40 equals 
.737, which is the efficiency of this dynamo. When 
testing dynamos it is usual to provide an artificial load 
which can be kept constant. Large metal plates, 
preferably copper, are connected to the positive and 
negative mains of the dynamo and immersed in a 
barrel of water. The quantity of current that will flow 
from one plate to the other can be regulated by dis¬ 
solving more or less salt in the water and by immers¬ 
ing the plates more or less and also by bringing them 
closer together. The greater the surface of the plates 
immersed in the water and the nearer they are brought 
together, the greater will be the current. Be very care¬ 
ful and do not let the plates touch each other. Before 


190 


ELECTRICITY FOR ENGINEERS 


accepting a new dynamo a test run of twenty-four 
hours at full load is usually made and the water rheo¬ 
stat need be used only to keep the load constant when 
lights are switched on or off. 

Photometer. The amount of light given off by an 
incandescent lamp is measured in candlepower. To 
determine the candlepower of a lamp, an appaiatus 
known as the photometer is used. Fig. 106 shows a 
diagram of what is known as the Bunsen photometer. 
S is a scale divided into inches, meters, or any suitable 
divisions, at one end of which is placed a standard 
lamp and at the other end the lamp to be measured. 


(B) 


(g) 


n - ! r i" t r 1 ■] 1 1 

1 i~i i r'rTN^i ' 1 

I | I ! 1—i i—n i 




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1 1 1 L 1 11 1 1 1 1 1 

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FIGURE 106 . 


A small screen, made of white paper having a grease 
spot in the center, is mounted on a stand so that it can 
be moved along the scale. To operate the instrument, 
move the screen to such a point that the grease spot 
becomes, invisible from either side. The two candle- 
powers are now to each other as the squares of their 
distances from the screen. For instance, suppose the 
lamp A is a standard 16 candlepower lamp and at the 
point where the grease spot is invisible the distance 
from B to the screen is 20 in., and from A to the 
screen 40 in., then B is to A as 20 squared is to 40 
squared, or as 400 is to 1,600 or one-fourth as 
great; therefore B is a 4 candlepower lamp. Care must 

































ELECTRICITY FOR ENGINEERS 


191 


be taken that the two lamps are burning at just the 
proper voltage, otherwise the comparison will not be 
accurate. Instruments of the kind just described are 
made in a variety of different patterns, but their prin¬ 
ciple remains the same. Candlepowers may also be 
compared by a method known as Rumford’s. Take a 
pencil or other opaque rod and place it in front of a 
white piece of paper or light-colored wall. Now place 




figure 107 . 


in front of it, but separated so that there will be two 
separate shadows cast, the two lamps to be compared. 
By moving one of the lamps away from, or closer to, 
(he screen, at some point the two shadows will become 
of the same density. Now measure the distances of the 
two lamps from the screen, and their candlepowers 
will be to each other as the squares of the distances; 
(Fig. 107). 



































192 


ELECTRICITY FOR ENGINEERS 


If the current consumed by a lamp and the voltage 
maintained at its terminals are measured by an amme¬ 
ter and voltmeter, as shown in Fig. 106, we need only 
find' the watts (current times volts) and divide by the 
candlepower to find the efficiency of the lamp. If, for 
instance, the 4 candlepower lamp B is taking ^ ampere 
at no volts, we have 18 Yi watts expended on it; this 
divided by the candlepower 4 shows an efficiency of 
4 t \ watts per candle. 


CHAPTER XIII 


Storage Batteries. The storage battery is often 
referred to as an accumulator. * An accumulator is an 
appliance for storing electricity. It depends upon the 
chemical changes undergone by certain substances 
when subjected to the action of an electric current. 
Strictly speaking, it is not correct to say that electri¬ 
city is stored in an accumulator, although as far as 
external results is concerned such appears to be the 
case. What it really does is this: The current flowing 
into the accumulator produces a gradual chemical 
change or decomposition of the active elements of 
which the battery is constructed. This change con¬ 
tinues to take place as long as the charging current is 
applied. This is known as electrolytic action. As soon 
as the current ceases, so also does the chemical decom¬ 
position of the elements cease, and if the terminals be 
then connected by a wire, a reversal of the chemical 
process commences. Particles gradually reform them¬ 
selves into original chemical combinations, and by so 
doing produce a current of electricity which flows in 
opposite direction to that originally used for charging. 

An early form of accumulator, though more of 
experimental than practical interest, w r as Grove’s gas 
battery. This was composed of a series of cells, each 
cell comprising two tubes, closed at the upper ends, 
and dipping down into a glass jar containing acidu¬ 
lated water. Each tube had a platinum wire fused into 
the closed end, from which a strip of platinum foil 
extended downwards into the liquid. The outer ends 

193 


194 


ELECTRICITY FOR ENGINEERS 


of the platinum wires were provided with terminals, by 
means of which several of these cells were connected 
together. A charging current was then applied and 
resulted in the gradual decomposition of the water in 
the various glass jars. Hydrogen collected on one of 
the platinum plates in each of the cells and oxygen on 
the other. If after a short time the charging source 
was disconnected from the wires joined to the outer 
terminals of the cells and a galvanometer substituted, 
it was found that a current would then flow in the 
reverse direction until all the separated hydrogen and 
oxygen gases had recombined to form water again. 

From a practical point of view the gas battery was 
deficient, inasmuch as it would only supply current for 
a very short time, and several workers set themselves 
the task of contriving an arrangement to obviate this 
defect. The most successful of these early workers 
was Plante, and he found in the course of his experi¬ 
ments that the best results were to be obtained by 
using lead plates or electrodes in a dilute solution of 
sulphuric acid. He made a cell by taking two long 
strips of sheet lead, placed one over the other with 
pieces of insulating material between, and coiling 
these up into spiral form. These plates were provided 
with separate terminals and were placed in a jar con¬ 
taining a solution of sulphuric acid. The action of the 
charging current was to decompose the water in the 
solution, the oxygen combining with the metal of the 
positive plate and thus forming peroxide of lead, 
whereas the hydrogen was simply deposited on the 
negative plate and there remained in gaseous form. 
On discontinuing the charging current, the hydrogen 
combined with the oxygen in the solution to form 
water again, while the peroxide of lead was deoxidized, 


ELECTRICITY FOR ENGINEERS 


195 


the lead remaining on the surface of the plate as 
spongy lead, and the oxygen reentered the solution to 
compensate for the oxygen which was extracted there¬ 
from by the hydrogen in forming water. Plante found 
that this method of construction enabled him to get an 
electromotive force of from 2 to 2.5 volts, as against 
1.47 volts given by Grove’s gas battery. 

Plante’s experiments did not, however, terminate 
with this achievement, and he next introduced a 
method for considerably increasing the available 
metallic surface of the electrodes. This plan is known 
as “forming” the plates, and consists of repeating for 
a considerable time the following series of operations: 
(1) charge the accumulator, (2) discharge ditto, (3) 
recharge, but with the charging current entering in the 
reverse direction, (4) again discharge. This series of 
reversals in charging and discharging, if kept up for 
several days, has the effect of causing the lead plates 
to become very porous or spongy in character, and, 
therefore, by reason of the additional surface of con¬ 
tact between electrolyte and electrode thus provided, 
enables the cell to retain a much greater charge than 
it would otherwise. 

It is not difficult to see that this work of forming 
is of a somewhat tedious and expensive character, and 
with the object of reducing this process to a minimum, 
another inventor, Faure, conceived the idea of using 
plates coated with a paste of lead-oxide, a plan which 
made it possible to use an accumulator with success 
after being charged only two or three times. When first 
introduced, some difficulty was found in making the 
lead-oxide paste adhere properly to the plates, and 
various means were devised to overcome this drawback. 
Scratching and indenting the lead plates was tried, 


196 


ELECTRICITY FOR ENGINEERS 


but this was ultimately superseded by the plan of 
making perforated plates in the form of grids, the 
paste being pressed into the perforations. With vari¬ 
ous slight modifications, in the shape of perforations, 
this device has been found to answer exceedingly well, 
and is now very generally adopted. 

When an accumulator is freshly charged, it would be 
found to have an electromotive force of about 2.25 to 
2.5 volts, but after being used a short time this falls to 
about 2 volts, at which figure it remains until the cell 
is nearly exhausted. For many purposes, however, a 
higher voltage than this is required, and it then 
becomes necessary to have several cells joined in 
series, so as to give a total voltage equal to the 
number of cells multiplied by 2. Thus 20 cells of 2 
volts each, if joined in series, would give an electro¬ 
motive force of 40 volts; 50 cells would give 100 volts, 
and so on. 

The quantity of current which a cell will accumulate 
or store depends upon the area of its plates; the larger 
the plates the greater the capacity of the cell, and the 
higher the permissible rate of discharge. As it is not 
always convenient to use very large plates where great 
capacity is required, the same result may be obtained 
by using a number of small plates to increase the 
available plate surface, but in such cases the plates 
must be connected in parallel. That is, the positive 
plates must all be connected to one terminal, and the 
negative plates all to the other terminal, thus forming 
practically two plates divided into a number of 
branches. 

The capacity of an accumulator is usually measured 
in ampere hours. Thus an accumulator which will 
discharge a current of ten amperes for one hour, or of 


ELECTRICITY. FOR ENGINEERS 


197 


five amperes for two hours, or of one ampere for ten 
hours, is said to have a capacity of ten ampere hours. 
As a general rule, it maybe estimated that an accumu¬ 
lator has a capacity of six ampere hours for each 
square foot of positive plate surface. 

For charging storage batteries the shunt dynamo is 
generally used, and the voltage must be kept as nearly 
constant as possible. Fig. 108 shows a very simple 
installation where the battery is intended to be charged 
during the running time of the dynamo and to carry 
the lights during such time as the dynamo is not in 



action. The ammeter A, in the battery line, should 
be of a kind which indicates the direction of the cur¬ 
rent passing through it. The rheostat R is used to 
regulate the charging current and the voltmeter V is 
connected so that either the voltage of the dynamo or 
the battery may be taken. In addition to this volt¬ 
meter a low reading meter should also be provided to 
test single cells. An automatic circuit breaker is also 
often provided to open the circuit should the current 
through it flow in the wrong direction. Should, for 
any reason, the voltage of the dynamo fall below that 








































































198 


ELECTRICITY FOR ENGINEERS 


of the battery while charging, the battery would begin 
to discharge through the dynamo. Where it is import¬ 
ant that the voltage supplied by the battery shall be 
at the same voltage as that supplied by the dynamo, a 
“booster” is employed to help charge the battery. 
Such a booster increases the electromotive force at 
the terminals of the battery sufficient to allow it to be 
charged to the full pressure of the dynamo. In setting 
up and charging storage batteries, detailed instructions 
should be obtained from the makers and rigidly 
followed. 


CHAPTER XIV 


Electrolysis. Electrolysis is chemical decomposition 
effected by means of the flow of an electric current. 
By electrolytic action it is possible to deposit metals, 
such as gold, silver, nickel, etc., over the exterior 
surface of other metals. This process is ordinarily 
called nickel plating, gold plating, etc., and is carried 
on by means of tanks in which there are liquids hold¬ 
ing in solution some of the various metallic salts. By 
placing over these tanks a bar or number of bars made 
of brass or copper, we may hang articles from these 
bars by means of wires, so that they are submerged in 
the solution. Now by using a dynamo whose output 
is low in pressure or electromotive force and high in 
quantity or amperes, and connecting the positive or 
outgoing terminal of this machine to a piece of metal, 
such as copper, nickel, gold, or silver, and submerging 
this metal in the liquid contained in the tank, the flow 
of current from this piece of gold or silver into the 
liquid or bath will carry with it, by electrolysis or 
electrolytic action, some of this gold or silver and 
deposit it on the articles suspended in the liquid, from 
the brass or copper bars to which the negative terminal 
of the plating dynamo is connected. The use of the bath 
containing metallic salts reduces the resistance from 
the metal to be deposited on the articles that are to be 
plated, which are the negative electrodes. This effects 
an equal deposit of metal over the entire surfaces 
being subjected to the electrolytic or plating action. 

Where it is desired to cover such metals as steel or 

199 


200 


ELECTRICITY FOR ENGINEERS 


iron with silver or gold, it becomes necessary to subject 
the articles to be plated to what is called a striking 
bath. This striking bath consists of a system of elec¬ 
trolytic action as above described, where copper is first 
deposited over the surfaces of iron or steel. The more 
precious metals will distribute themselves over this 
copper surface more uniformly and in a finer grained 
manner than if the article had not been copper plated 
first. After the plated article has had sufficient metal 
deposited on its surface, it is put through a buffing and 
polishing process for its final finish. 

Electrolysis has also been applied where it is desired 
to reclaim the precious metals from ores without smelt¬ 
ing them. This method consists of immersing the ore 
in tanks filled with a solution. The ore receives cur¬ 
rent from the positive element of a dynamo through 
the liquid solution, and the metal in the ore is depos¬ 
ited on the negative plate in the vat, which is con¬ 
nected to the negative terminal of the dynamo. Thus 
by employing a process similar to electro plating it is 
possible to extract the metal from the ores in almost 
its pure state from the negative plate. The solution 
mentioned is water in which various kinds of metallic 

salts have been dissolved which bear a chemical rela- 

♦ 

tion to the metals to be extracted. 

This short description will assist in explaining how 
electrolytic action takes place in water and gas pipes 
buried under the surface of the ground, when, for 
instance, electric railroads, operated in the vicinity 
are not properly constructed. In the construction of 
an electric street railroad or trolley line the generators 
are connected to the trolley wires usually at the posi¬ 
tive terminals of the dynamos. 

The current passes from the trolley line through the 


ELECTRICITY FOR ENGINEERS 


201 


car to the rails and back to the negative pole of the 
dynamo. If the rails are not of sufficient carrying 
capacity, or if there is a pipe line of better carrying 
capacity near the rails, it is quite certain that some of 
the current will be carried by the pipes. Wherever 
the current leaves a pipe it carries some of the metal 
with it, and if there is much current a hole will soon 
be eaten into the pipe. As the pipes are mostly 
covered with rust, which is a partial insulator, the 
current will be most likely to enter and leave the pipe 
at some point which is comparatively bright and the 
electrolytic action will be concentrated at such points. 

Heating by Electricity. The electric heater is simply 
a coil of wire through which enough current is caused 
to flow to produce quite an appreciable amount of 
heat. In the use of resistance coils for nearly all elec¬ 
trical purposes the function of the resistance coil is to 
cut down the flow of current required at some point, as 
for instance, where a resistance coil is used as a start¬ 
ing box on a motor. The flow of current across or 
through such a coil or coils, will produce heat, and 
shows one way in which electric power can be con¬ 
verted into heat. Another instance, if a contact is 
poorly made, the resistance to the flow of current 
offered by this contact produces heat and a consequent 
loss of watts. The voltaic arc in an arc lamp is 
another instance where resistance to the flow of current 
is interposed in the circuit and consequently produces 
heat. 

The incandescent lamp is another instance where 
resistance is the cause of the production of heat, but, 
of course, in both the arc and incandescent light, the 
result desired is a maximum amount of light with a 
minimum amount of heat. 


202 


ELECTRICITY FOR ENGINEERS 


If we were to construct a coil of small wire, whose 
total resistance would be the same as that of another 
coil of large wire, it would be found that the coil of 
small wire would contain much less wire than the coil 
of large wire, both resistances being the same in ohms. 
Now if both these coils were connected across a circuit, 
we will say of iio volts, the same amount of current 
would flow over both the coils, because their resist¬ 
ances are alike, but the smaller coil would get quite 
hot, while the larger coil would perhaps be just 
slightly warmed. The number or quantity of heat 
units gi en out by both coils are the same. The sur¬ 
face from which these heat units pass out into the 
atmosphere is much less in the smaller coil than in the 
large one, hence the smaller coil gets quite hot, some¬ 
times even red hot. If we were to permit current to 
flow over this small coil and maintain its temperature 
at a low red heat, it would in time become oxidized by 
the chemical action of the oxygen in the air. To pre¬ 
vent this oxidization we may imbed this small coil in 
a porcelain cement, and after it has been properly 
imbedded in this cement we will put the entire coil 
and cement through a baking process, making the 
cement quite hard and sealing the wire coil from the 
influence of the oxygen in the atmosphere. Then 
we can take this coil so constructed and produce 
heat in a flat iron, or in a stove, in a curling iron, 
soldering iron, and in fact anywhere. The coil being 
so hermetically se*aled it can also be used in chafing 
dishes, tea kettles, water urns, glue pots, etc. The 
principle of producing heat by electricity remains the 
same no matter where or how it is applied, the only 
difference necessary being in the form given to the 
heater coils. 


ELECTRICITY FOR ENGINEERS 


203 


Heating by electricity is quite an'* expensive and 
uneconomical proposition, and an idea can be obtained 
as to the quantity of current necessary to do electric 
heating, when we consider that in very cold weather it 
requires nearly as much power to operate the heaters 
in a street car system as it does to propel the cars. 


* 


CHAPTER XV 


Lightning Arresters. Lightning arresters are needed 
on overhead, outdoor lines only. The simplest form 
of lightning arrester consists of two bare metal plates 
set very close together, but under no circumstances 
allowed to touch each other. (See P'ig. 109.) One of 
these plates is connected to the overhead line and the 
other to the ground. 

A sudden flow of current meets with an enormous 
opposition when it encounters the coils of a large 
electro magnet. Although the resistance of the air 
space between the two plates forming the lightning 
arrester may be several millions of ohms, it is far 
easier for the current to jump this air space in such a 
very short time as is taken up by a lightning discharge 
than it would be to force its way around the coils of 
the magnet. The reason for this is, that a current of 
electricity flowing through the coils of an electro mag¬ 
net creates magnetism or lines of force. These lines 
of force cut through the coils on the magnet and in 
that way tend to produce a counter current, or counter 
electromotive force, which, for a very short time, is 
almost equal to the electromotive force creating it. 
Were the current flow to continue for any appreciable 
time this counter electromotive force would disappear 
entirely as soon as the magnetism reached its final 
strength. 

In order, therefore, to facilitate as much as possible 
a lightning discharge towards the ground and away from 
the machinery and buildings, the wires leading from 

204 


ELECTRICITY FOR ENGINEERS 


205 


the arresters to the earth should be run in as straight a 
line as possible and be kept well separated from metal 
parts, especially iron, of the building. Under no cir- 



LINE 



\ 


vwwvwwvwwv 

/VWVWVWVWVVVN. 


V. 



TO 

GROUND 


FIGURE 109 . 

cumstances should the ground wire be run in an iron 
pipe, nor should lead covered wires be used. 

With the simple lightning arrester shown above there 
is great liability of the current from the dynamo fol¬ 
lowing the arc caused by the lightning discharge to 
















206 


ELECTRICITY FOR ENGINEERS 


ground, and, as there must be two arresters, one on each 
side of the dynamo, this amounts almost to a short 
circuit and is very likely to put the dynamo out of 
service. Should such an arc continue for a few min¬ 
utes, it may fuse the plates of the arrester. The arc 
can readily be extinguished by blowing it out or caus¬ 
ing a strong blast of air to strike it. 

To prevent trouble of this kind the Thomson Jight- 



figure 110. 


ning arrester, shown in Fig. iio, was devised. This 
consists of the two diverging metal plates shown at 
the top of the figure, one of which is connected to the 
earth and the other to the line to be protected and an 
electro magnet, as shown. The current from the 
dynamo traverses the coils of the electro magnets. 
The action is as follows: When a lightning discharge 
through the arrester takes place, it forms an arc 





ELECTRICITY FOR ENGINEERS 


£07 


between the lower points of the plates above the mag¬ 
nets. These plates are very close together at the 
bottom. Now the electric arc is always strongly 
repulsed by a magnet, and hence the arc formed is 
forced upward where the plates diverge, and the space 
becomes too great for it to be maintained and it is 
then broken. The arc is virtually blown out by the 
magnetism. 


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are such as delight the infantile mind, and the 
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the selections are new and fresh, many being spe¬ 
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LITTLE FOLKS’ DIALOGUES & DRAMAS. 

By Charles "W alter Brown, A. M. A collection of 
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heartily recommend this book to amateurs and 
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many pages, and comedians and amateurs who 
wish to keep an audience or social gathering in a 
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IRISH WIT AND HUMOR. j£*r W iJVteS 

tor in human experience which the world can ill 
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CONUNDRUMS AND RIDDLES. 

Collected and arranged by John Kay This is 
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NEGRO MINSTRELS. By Jack Haverly. A 

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with the brightest dialogue between “Tambo,” 
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of ballads, songs, gags, conundrums, side-splitting 
stump speeches, etc. Mr. Jack Haverly was one of 
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TOASTS AND AFTER DINNER SPEECHES. 

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on various subjects. Prom this book you may learn 
some lessons that will prove profitable when called 
upon to speak or respond to some toast or senti¬ 
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Not only is it valuable to the novice, but the ex- 

{ •erienced orator will find many good suggestions. 
80 pages. 

.25 Cents 

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MODERN QUADRILLE CALL BOOK AND 
COMPLETE DANCING MASTER. By a.c. 

Wir th, 

President of the American National Association of 
Masters of Dancing. 

Containing all the new modern square dances and 
tabulated forms for the guidance of the leader of 
others in calling them, full and complete direc¬ 
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such as Plain Quadrilles, Polka Quadrilles, Prairie 
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8 uadrille, Dixie Figures, Girl I Left Behind, Old 
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In the Round Dances a special feature consists of 
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CHAS. K. HARRIS’ COMPLETE SONGSTER. 

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STANDARD DRILL & MARCHING BOOK. 

By Edwin Ellis. Containing an endless variety 
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ZANCIG’S new complete palmistry. 

The only authorized edition published. By Prof, 
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THE GYPSY WITCH DREAM BOOK. 

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A BOOK EVERY ENGINEER AND ELECTRICIAN 
SHOULD HAVE IN HIS POCKET. A COMPLETE 
ELECTRICAL REFERENCE LIBRARY IN ITSELF 


NEW EDITION 

'Id he Harvdy Vest-Pocket 


ELECTRICAL 

DICTIONARY 



BY WM. L. WEBER, M.E. 

ILLUSTRATED 

C ONTAINS upwards of 4.800 words, 
terms and phrases employed in the 
electrical profession, with itheir 
definitions given in the most concise, 
lucid and comprehensive manner. 

The practical business advantage 
and the educational benefit derived 
from the ability to at once understand 
the meaning of some term involving 
the description, action or functions of 
a machine or apparatus, or the physi¬ 
cal nature and cause of certain phe¬ 
nomena, cannot be overestimated, and 
will not be, by the thoughtful assidu¬ 
ous and ambitious electrician, because 
he knows that a thorough understand¬ 
ing, on the spot, and in the presence 
of any phenomena, effected by the aid 
of his little vest-pocket book of refer¬ 
ence, is far more valuable and lasting 
in its impression upon the mind, than 
any memorandum which he might 
make at the time, with a view to the 
future consultation of some volumin¬ 
ous standard textbook, and which is 
more frequently neglected or,forgotten 
than done. 

The book is of convenient size for 
carrying in the vest pocket, being only 
2% inches by 5*4 inches, and M inch 
thick; 224 pages, illustrated, and 
bound in two different styles: 


New Edition. Cloth, Red Edges, Indexed . . 25c 
New Edition. Full Leather, Gold Edges, Indexed, 50c 


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THE NEW AIR BRAKE BOOK Invaluable to Trainmen, Engineers 
Firemen, Conductors, Electric Motormen and Mechanics. 

The Latest and Best 1904 Edition. 

MODERN AIR BRAKE PRACTICE 

ITS USE AND ABUSE 

With Questions and Answers for Locomotive Engineers and Electric 
Motormen. By FRANK H. DUKESMITH. 



T 1 


|HE necessity for a modern, practical air 
brake instruction book was never 
greater than now, owing to the fact 
that railroad extension is being so ag¬ 
gressively pushed in all parts of America, 
and particularly because of the fact that 
recent legislation of our An erican congress, 
compelling railroads to bring up their air 
brake equipment to at least 50 per cent of 
the number of cars in service, is naturally 
causing all railroads to demand a greater 
efficiency on the part of their employes in 
the operation and maintenance of the 
automatic air brake. 

While there have been many air brake 
bool^s written, we feel safe in saying that 
never before has the subject been treated in 
the same lucid, understandable manner in 
which our author has treated it in this new 
book. 

Mr. Dukesmith treats the subject en¬ 
tirely different from all other air brake 
writers, inasmuch as he has divided the 
subject into three distinct parts, as follows: 
In section one, he explains and illustrates 
the various parts of the air brake equip¬ 
ment and their duties: in section two, he 
treats of the various defects and their remedies: in section three, he treats of 
the philosophy of airbrake handling, together with tables and rules for com¬ 
puting brake power, leverage, etc. 

E. ery device now in use in the Westinghnuse Air Brake System is fully explained 
and particular treatment is given the subject of the high speed biake in its pres¬ 
ent stage of development. 

In the addition to the Westinghous* 1 automatic airbrake, there is also given 
a full and complete treatment of the straight air brake as is note used on electric 
railways, in order that motormen may be aide to master the necessary knowledge 
demanded of them in handling air brakes. 

Following each section is a complete list of questions and answers covering 
a thorough air brake examination. 

“Modern Air Brake Practice, Its Use and Abuse" contains over two hundred 
and fifty pages and is profusely illustrated with engravings of all parts of the 
air brake equipment, and, as these engravings have been furnished by the West- 
ingliouse Air Brake Company of Pittsburg, Pa., absolute authenticity is 
assured. 

You may have read many air brake books, but whether you have or not, 
you cannot afford to be without the benefits contained in this volume,if you have 
anything whatever to do with the operation or maintenance of air brakes. 

The book is fully indexed and cross indexed, so that any subject can be 
turned to immediately, as desired. 

If you are already posted, you can becomebetter posted. If you really want 
to know all that is worth knowing about air brake practice send for this book. 


$1.50 


12MO. CLOTH. PRICE ONLY. 

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DYNAMO TENDING 



ENGINEERS 

Or, ELECTRICITY 
FOR STEAM ENGINEERS 

By HENRY C. HORSTMANN and 
VICTOR H. TOUSLEY, 

Authors of “Modern Wiring Diagrams and 
Descriptions for Electrical Workers.” 


This excellent treatise is written by 
engineers for engineers, and is a clear 
and comprehensive treatise on the prin¬ 
ciples, construction and operation of 
Dynamos, Motors, Lamps, Storage Bat¬ 
teries, Indicators and Measuring Instru¬ 
ments, as well as full explanations of the 
principles governing the generation 
of alternating currents and a descrip¬ 
tion of alternating current instruments and machinery. There are 
perhaps but few engineers who have not in the course of their labors 
come in contact with the electrical apparatus such as pertains to light 
and power distribution and generation. At the present rate of increase 
in the use of Electricity it is but a question of time when every steam 
installation will have in connecton with it an electrical generator, even 
in such buildings where light and power are supplied by some central 
station. It is essential that the man in charge of Engines, Boilers. 
Elevators, etc., be familiar with electrical matters, and it cannot well 
be other than an advantage to him and his employers. It is with a view 
to assisting engineers and others to obtain such knowledge as will enable 
them to intelligently manage such electrical apparatus as will ordinarily 
come under their control that this book has been written. The authors 
have had the co-operation of the best authorities, each in his chosen field, 
and the information given is just such as a steam engineer should know, 
To further this information, and to more carefully explain the text, 
nearly 100 illustrations are used, which, with perhaps a very few excep¬ 
tions, have been especially made for this book. There are many tables 
covering all sorts of electrical matters, so that immediate reference can 
be made without resorting to figuring. It covers the subject thoroughly, 
but so simply that any one can understand it fully. Any one making a 
pretense to electrical engineering needs this book. Nothing keeps a man 
down like the lack of training; nothing lifts him up as quickly or as 
surely as a thorough, practical knowledge of the work he has to do. This 
book was written for the man without an opportunity. No matter what 
he is, or what work he has to do, it gives him just such information 
and training as are required to attain success. It teaches just what 
the steam engineer should know in his engine room about electricity. 
12rao, Cloth, 100 Illustrations. Size5i4x7%. PRICE NET PA 
Sold by booksellers generally, or sent, all charges paid, upon $I»UU 
receipt of price ■ 

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Publishers of Self-Educational Books for Mechanics 

211-213 East Madison Street CHICAGO, U.S.A. 



















Easy Electrical Experiments 

i—W—— I ■MMBMU-IH — Ml , III! !■ II ■ I I I ■■III! — ■—■I——— 

and How to Make Them 


By L. P. DICKINSON 

This is the very latest and most 
valuable work on Electricity for the 
amateur or practical Electrician pub¬ 
lished. It gives in a simple and 
easily understood language every 
thing you should know about Gal¬ 
vanometers, Batteries, Magnets, In¬ 
duction, Coils, Motors, Voltmeters, 
Dynamos, Storage Batteries, Simple 
and Practical Telephones, Telegraph 
Instruments, Rheostat, Condensers, Electrophorous, 
Resistance, Electro Plating, Electric Toy Making, etc. 

The book is an elementary hand book of lessons, 
experiments and inventions. It is a hand book for 
beginners, though it includes, as well, examples for 
the advanced students. The author stands second to 
none in the scientific world, and this exhaustive work 
will be found an invaluable assistant to either the 
6tudent or mechanic. 

Illustrated with hundreds of fine drawings; printed 
on a superior quality of paper. 

J2mo Cloth. Price, $1.25. 

Sent postpaid to any address upon receipt of price. 

FREDERICK J. DRAKE CO. 

P UBLISHE US ^ 

3 3 3 ^ ChiQ&go 













Modern Carpentry 

A PRACTICAL MANUAL 

T— ——■ ! !■ I I - —■— ——1— — —I ■■■ ■■■I. I —■^T 

FOR CARPENTERS AND WOOD WORKERS GENERALLY 


y I’red T. Hodgson, Architect, Editor of the National Builder, Practical 
Carpentry, Steel Square and Its Uses, etc., etc. 

/V NEW, complete guide, containing hundreds of quick 
methods for performing work in carpentry, joining and 
general wood-work. Like all of Mr. Hodgson’s works, it is 
written in a simple, every-day style, and 
does not bewilder the working-man 
with long mathematical formulas or 
abstract theories. The illustrations, of 
which there are many, are explanatory, 
so that any one who can read plain 
English will be able to understand them 
easily and to follow the work in hand 
without difficulty. 

The book contains methods of laying 
roofs, rafters, stairs, floors, hoppers, 
bevels, joining mouldings, mitering, 
coping, plain hand-railing, circular 
work, splayed work, and many other 
things the carpenter wants to know to help 
him in his every day vocation. It is the 
most complete and very latest work published, being thorough 
practical and reliable. One which no carpenter can afford .c 
be without. 

The work is printed from new, large type plates on a superior qualify 
of cream wove paper, durably bound in English cloth. 

Price - $1.00 

FREDERICK J. DRAKE & CO. 

211-213 E. Madison St., Chicago. 











































































Fred T. Hodgson's New (1903) Books For Builder? 


STEEL SQUARE 

A TREATISE OF THE PRACTICAL OSES CF 

By FRED. T. HODGSON, Architect. 

.New and up-to-date. Published May 1st, 1903. Do not mistake this edition 
for the one published over 20 years ago. 

This is the latest practical work on 
the Steel Square and its u>es pub- 
ished. It is thorough, accurate, clear 
and easi y understood. Confounding 
terms and phrases have been relig¬ 
iously avoided where possible, 
and everything in the book has been 
made eo plain that a boy twelve yea’-s 
of age, possessing ordinary intelli¬ 
gence, can understand it from begin¬ 
ning to end. 

It is an exhaustive work including 
some very ingenious devices for laying 
out bevels for rafters, braces and other 
inclined work; also chapters on tl e 
Square as a calculating machine, show¬ 
ing how to measure Solids, Surfaces 
and Distances—very useful to builders 
and estimators. Chapters on roofing' 
and how to form them by the aid of 
the. Square. Octagon, Hexagon, Hip 
and other roofs are shown and ex¬ 
plained, and the manner of getting 
tho rafters and jacks given. Chapters 
on heavy timber framin g, s- howin g how 
the Square is used for laying out Mor¬ 
tises, Tenons, Shoulders, Inclined 
Work, Angle Corners and similai 
work. The work also contains a large number of diagrams, showing how 
the Square may be used in finding Bevels, Angles, Stair Treads and bevel 
cuts fur Hip, valley, Jack and other Rafters, besides methods for laying 
out Stair Strings, Stair Carriages and Timber Structures generally. Also 
con tains 25 beautiful halftone illustrations of the perspective and floor plans 
of 25 medium priced houses. 

The work abounds with hundreds of fine illustrations and explana¬ 
tory diagrams which will prove a perfect mine of instruction for tho 
mechanic, young or old. 

Two large volumes, 560 pages, nearly 500 illustrations, printed on a 
superior quality of paper from new large type. 


Price, 2 Vols., cloth binding.$2.00 

Price, 2 Vols., half=l< ather binding. 3.00 

Single Volumes, Part 1, cloth. 1.00 

“ “ Part I,half-leather. 1.50 

“ “ Part II, cloth. 1.00 

" *“ Part II, one half-leather. 1.51 


SEND FOR COMPLETE ILLUSTRATED CATALOGUE FREE 

FREDERICK J. DRAKE (EL CO. 

PUBLISHERS OF SELF-EDUCATIONAL BOOKS 

211 E. MADISON STREET V V CHICAC^ 




































































































i 


Best and Most Complete Book on Engineering and Electricity 
puDlisnea. \\ ritten by practical Engineers and Electricians in a wav 
that you can understand it. UP-TO-DATE 1904 EDITION. 

Ghe 20th Century Hand Book 

--- poR —-- 

Engineers and Electricians 



A‘ 


COMPENDIUM 
of useful knowl¬ 
edge appertain¬ 
ing to the care and 
management of Steam 
Engines, Boilers and 
Dynamos. Thorough¬ 
ly practical with full 
instructions in regard 
to making evapora¬ 
tion tests on boilers. 
The adjustment of the 
slide valve, corliss 
valves, etc., fully de¬ 
scribed andillustrated, 
together with the ap¬ 
plication of the in¬ 
dicator and diagram 
analysis. The subject 
of hydraulics for en- 
g i n e e r s is made a 
special feature, and all problems are solved in plain figures, thus ena¬ 
bling the man of limited education to comprehend their meaning. , 

By C. F. SWINGLE, M.E. 

Formerly Chief Engineer of the Pullman Car Works. Late Chief Engineer 
of the Illinois Car and Equipment Co., Chicago. 


ELECTRICAL DIVISION 

The electrical part of this valuable volume was written by a practical 
engineer for engineers, and is a clear and comprehensive treatise on the 
principles, construction and operation of Dynamos, Motors, Lamps, 
Storage Batteries, Indicators and Measuring instruments, as well as an 
explanation of the principles governing the generation of alternating cur¬ 
rents, and a description of alternating current instruments and machin¬ 
ery. No better or more complete electrical part of a steam engineer’s 
book was ever written for the man in the engine room of an electric 
lighting plant. 

SWINGLE’S 20 th CENTURY HAND BOOK 


FOR. ENGINEERS AND ELECTRICIANS 


Over 300 illustrations; handsomely bound in full leather pocket C 

book style; size 5 x6% x 1 inch thick. PRICE NET . . . . VbiOU 


Sold by booksellers generally or sent postpaid to any 
address upon receipt of price. 


FREDERICK J. DRAKE G) COMPANY 

Publishers of Self-Educational Books for Mechanics 

2II-2I3 East Madison Street CHICAGO, U.S.A. 


































'JU 








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